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5.7C: The Pentose Phosphate Shunt - Biology

5.7C: The Pentose Phosphate Shunt - Biology



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Leerdoelwitte

  • Gee 'n uiteensetting van die twee hooffases van die pentosefosfaat shunt: oksidatiewe en nie-oksidatiewe fases

Die pentosefosfaatweg (PPP; ook die fosfoglukonaatweg genoem en die heksose monofosfaat shunt) is 'n proses wat glukose-6-fosfaat in NADPH en pentoses (5-koolstof suikers) afbreek vir gebruik in biologiese prosesse stroomaf. Daar is twee verskillende fases in die pad: die oksidatiewe fase en die nie-oksidatiewe fase. Die eerste is die oksidatiewe fase waarin glukose-6-fosfaat omgeskakel word na ribulose-5-fosfaat. Tydens hierdie proses twee molekules NADP+word verminder tot NADPH. Die algehele reaksie vir hierdie proses is:

Glukose 6-fosfaat + 2 NADP++ H.2O → ribulose-5-fosfaat + 2 NADPH + 2 H+ + CO2

Die tweede fase van hierdie weg is die nie-oksidatiewe sintese van 5-koolstof suikers. Afhangende van die toestand van die liggaam, kan ribulose-5-fosfaat omkeerbaar isomeriseer tot ribose-5-fosfaat. Ribulose-5-fosfaat kan alternatiewelik 'n reeks isomerisasies sowel as transaldolasies en transketolasies ondergaan wat lei tot die produksie van ander pentosefosfate, insluitend fruktose-6-fosfaat, eritrose-4-fosfaat en glyceraldehied-3-fosfaat (beide tussenprodukte in glikolise). Hierdie verbindings word gebruik in 'n verskeidenheid van verskillende biologiese prosesse, insluitend die produksie van nukleotiede en nukleïensure (ribose-5-fosfaat), sowel as sintese van aromatiese aminosure (eritrose-4-fosfaat).

Glukose-6-fosfaat dehidrogenase is die tempo-beheerde ensiem in hierdie pad. Dit word allosteries gestimuleer deur NADP+. NADPH-gebruiksweë, soos vetsuursintese, genereer NADP+, wat glukose-6-fosfaat dehidrogenase stimuleer om meer NADPH te produseer. By soogdiere kom die PPP uitsluitlik in die sitoplasma voor; Daar word gevind dat dit die aktiefste in die lewer, melkklier en bynierkorteks is. Die verhouding van NADPH:NADP+ is normaalweg ongeveer 100:1 in lewersitosol, wat die sitosol 'n hoogs-reduserende omgewing maak.

Die PPP is een van die drie hoof maniere waarop die liggaam molekules met verminderende krag skep, wat ongeveer 60% van NADPH-produksie by mense uitmaak. Alhoewel die PPP oksidasie van glukose behels, is die primêre rol daarvan anabolies eerder as katabolies, deur die energie wat in NADPH gestoor word, te gebruik om groot, komplekse molekules uit klein voorlopers te sintetiseer.

Daarbenewens kan NADPH deur selle gebruik word om oksidatiewe stres te voorkom. NADPH verminder glutathione via glutathione reductase, wat reaktiewe H omskakel2O2 in H.2O deur glutathione peroxidase. Byvoorbeeld, eritrosiete genereer 'n groot hoeveelheid NADPH deur die pentosefosfaatweg om te gebruik vir die vermindering van glutathion.

Kern punte

  • Daar is twee verskillende fases in die pad: die oksidatiewe fase en die nie-oksidatiewe fase.
  • In die oksidatiewe fase, twee molekules NADP+ word verminder tot NADPH, gebruik die energie van die omskakeling van glukose-6-fosfaat in ribulose-5-fosfaat. Hierdie NADPH -molekules kan dan elders in die sel as 'n energiebron gebruik word.
  • Die nie-oksidatiewe fase genereer 5-koolstof suikers, wat gebruik kan word vir die sintese van nukleotiede, nukleïensure en aminosure.
  • Die pentosefosfaatweg is 'n alternatief vir glikolise.

Sleutel terme

  • glikolise: Sellulêre afbraak van die eenvoudige suikerglukose om pyruviensuur en ATP as energiebron op te lewer.
  • NADPH: Nikotinamied adenien dinukleotiedfosfaat (NADP) wat elektrone dra en gebind is met 'n waterstof (H) ioon; die verminderde vorm van NADP+.
  • oksidatiewe stres: Skade aan selle of weefsel veroorsaak deur reaktiewe suurstofspesies.

Pentosefosfaatweg

Pentose fosfaat pad ook genoem HMP pad wat staan ​​vir Hexose Mono- Phosphate Pathway. Dit verskil baie van die ander roetes, waar dit nie ATP vrystel of ATP verbruik tydens die proses nie. Dit is 'n metaboliese weg wat in alle soorte selle en weefsels voorkom.

In die lewer word 30% glukose gemetaboliseer deur die Pentose -fosfaatweg. Die HMP -pad kom hoofsaaklik voor in die Sitoplasma. Dit produseer NADPH, waarvan die 50% deur die selle gebruik word vir die sintese van vetsure. Die NADPH-molekule neem ook deel aan die oksidatiewe stres-homeostase en sintese van sitochroom P450-ensieme.

Behalwe NADPH, produseer HMP -pad ook triose, pentoses en hexoses, ens., Waar die produksie van pentoses help met die nukleotiedsintese. In hierdie konteks leer u die betekenis, fases (oksidatiewe en nie-oksidatiewe fase) en die betekenis van die pentosefosfaatweg ken.

Inhoud: Pentosefosfaatweg

Geskiedenis

JaarWetenskaplikeOntdekkingDie Nobelprys gewen
1930'sOtto WarburgNADP ontdek tydens die oksidasie van glukose 6-fosfaat tot 6-fosfoglukonaat1931 in fisiologie of geneeskunde
1950'sEfraim Racker en Fritz LipmannOntdek die ko-ensiem-A1953 in fisiologie of geneeskunde

Betekenis van Pentosefosfaatweg

Pentosefosfaatweg word gedefinieer as die metaboliese pad wat in alle lewende organismes voorkom, en dit gebruik die eerste tussenproduk van glikolise, dit wil sê Glukose 6-fosfaat vir die produksie van NADPH (deur die vermindering van koënsiem NADP) en a Pentose suiker.

Fases

In die Pentosefosfaatweg is daar twee fases, naamlik oksidatiewe en nie-oksidatiewe.

  1. Oksidatiewe fase: Daar is oksidasie, dit wil sê 'n verlies aan elektrone tydens hierdie fase. Dit behels die oksidasie van glukose 6-fosfaat (6-C gefosforyleerde suiker) in ribulose 5-fosfaat (5-C gefosforyleerde suiker).
  2. Nie-oksidatiewe fase: Hierdie fase behels nie die oksidasieproses nie. In hierdie fase tree ribulose 5-fosfaat op as 'n tussenproduk wat verskeie gefosforileerde koolhidrate produseer, wat dan deelneem aan die sintese van nukleotiede, vetsure, ens.

Koolhidraatmetabolisme: Primêre metabolisme van monosakkariede

M.D. Brownleader,. P.M. Dey, in Plant Biochemistry, 1997

3.3.3 Regulering

Alhoewel die pentosefosfaatbaan glukose-6-fosfaat heeltemal in CO kan omskep 2 (sien Fig. 3.3 herwinning van die produk, fruktose-6-fosfaat na glukose-6-fosfaat), die meer gewone produkte is gliseraldehied-3-fosfaat en fruktose-6-fosfaat wat dan in glikolise sal ingaan. Die pad kan dus as 'n siklus funksioneer, afhangende van sellulêre vereistes.

Die oksidatiewe pentosefosfaatbaan skakel tussen 15 en 30% van heksosefosfaat om in gliseraldehied-3-fosfaat en CO2 in ertjie- en spinasiechloroplaste. Glukose-6-fosfaat dehidrogenase en 'n laktonase kataliseer die eerste toegewyde stap van die oksidatiewe pentose fosfaat pad wat 'n strategiese beheerpunt is. Dit is die belangrikste vertakking tussen glikolise en die oksidatiewe pentosefosfaatweg. Die produkte van die pentosefosfaatweg is krities afhanklik van sellulêre vereistes omdat epimerase, isomerase, transketolase- en transaldolase-gekataliseerde reaksies vrylik omkeerbaar is.

Glukose-6-fosfaat dehidrogenase aktiwiteit is onder growwe en fyn regulerende beheer. 'n Merkbare toename in sy aktiwiteit in gesnyde aartappelwortel tydens aërobiese respirasie is ook waargeneem. Aansienlike toenames in die aktiwiteit van glukose-6-fosfaat dehidrogenase is ook waargeneem na veroudering van wortel-, swede- en aartappelskyfies. Die chloroplast-isoenziem word beïnvloed deur die NADPH/NADP + verhouding, pH, Mg 2+ en vlakke van glukose-6-fosfaat. Ashihara & Komamine (1976) het glukose-6-fosfaatdehidrogenase van die hipokotiele van Phaseolus mungo saailinge en het getoon dat inhibisie deur NADPH omgekeerd verband hou met pH. Glukose-6-fosfaatdehidrogenase word ook deur ribulose-1,5-bisfosfaat geïnhibeer. Beheer van die chloroplast isovorm deur die NADPH/NADP + verhouding kan dus versterk word deur ribulose-1,5-bisfosfaat. Beide die sitoplasmiese en chloroplastiese isoforme van glukose-6-fosfaat dehidrogenase van ertjieblare word geaktiveer in die donker (lae NADPH/NADP +) ligreaksies van fotosintese genereer NADPH. Gluconaat-6-fosfaat dehidrogenase word ook sterk gerem deur NADPH en fruktose-2,6-bisfosfaat.

In die oksidatiewe pentosefosfaatweg word NADPH gevorm deur die reaksies wat deur glukose-6-fosfaatdehidrogenase en glukonaat-6-fosfaatdehidrogenase gekataliseer word. Die Kek waardes van NADPH vir beide ensieme is onderskeidelik 11 μM en 20 μM en die pentosefosfaatweg word dus gereguleer deur die NADPH/NADP + verhouding. Behandeling van plantweefsels met metileenblou en nitraat, wat elektrone van NADPH aanvaar, stimuleer die oksidatiewe pentosefosfaatweg. Die verhouding NADPH/NADP + blyk die belangrikste faktor te wees wat die vloed deur die pentosefosfaatbaan reguleer. 'n Verminderde NADPH/NADP + verhouding behoort in beginsel 'n toename in sellulêre vraag na NADPH, aktivering van glukose-6-fosfaat dehidrogenase en 'n toename in die vloed deur die oksidatiewe pentose fosfaat pad aan te dui.

Die finale reaksies van die pentosefosfaatweg, gekataliseer deur ribosefosfaatisomerase, ribulosefosfaat 4-epimerase, transketolase en transaldolase is naby ewewig.

Of glukose-6-fosfaat die oksidatiewe pentosefosfaatweg of die glikolitiese weg in plantselle binnedring, is van kritieke belang vir ons begrip van respiratoriese glukosemetabolisme. Eksperimente wat 14 CO meet2 opbrengste en etiketteringspatrone van verskillende tussenprodukte dui daarop dat 5–15% van die respiratoriese glukosemetabolisme in plantselle deur die oksidatiewe pentosefosfaatweg verloop en waarskynlik nie 30% sal oorskry in verhouding tot glikolise nie. Die relatiewe hoeveelheid glukose wat gemetaboliseer word in die oksidatiewe pentosefosfaatweg en glikolise bly egter onduidelik.


Resultate

Cumenhidroperoksied is 'n uitstekende substraat vir glutathionperoksidase en 'n swak oksideermiddel. Ons het voorspel dat lae tot matige konsentrasies die vloei deur glutathionperoksidase sal verhoog, met 'n gevolglike toename in vloei deur die pentosefosfaatweg. Giftige effekte, wat by hoë konsentrasies verwag word, sal aangedui word deur 'n afname in die tempo van glikolise. Die toevoeging van 5 of 10 μM kumeenhidroperoksied het die basale vloei deur die pentosefosfaatweg met meer as 50% verhoog, maar het geen beduidende uitwerking op die tempo van glikolise gehad nie. Namate die kumeenhidroperoksiedkonsentrasie verder toegeneem het, het die vloei deur die pentosefosfaatbaan verminder en aansienlik minder geword by 160 μM in vergelyking met die piek by 10 μM en aansienlik minder by 640 μM in vergelyking met basale waardes (Fig. 1). Glikolitiese vloed was meer bestand teen kumeenhidroperoksied, en die eerste betekenisvolle afname is by 320 μM kumeenhidroperoksied gesien (Fig. 1). Onder hierdie toestande verteenwoordig pentosefosfaatwegvloei in die afwesigheid van kumeenhidroperoksied 'n bietjie minder as 1% van die totale hoeveelheid glukose wat deur glikolise gemetaboliseer is. Hierdie resultate is nie beïnvloed deur 'n lae-vlak leukosietbesmetting in die spermsuspensies nie, want vir eksperimente waarin spermsuspensies in twee verdeel is en een deel van leukosiete ontneem is deur behandeling met anti-CD45-bedekte Dynabeads, is die resultate van die ongeskonde en die leukosiet-uitgeputte suspensies was identies (data nie getoon nie).

Uitwerking van toenemende konsentrasies kumeenhidroperoksied op die metabolisme deur (a) die pentose fosfaat en (b) die glikolitiese weë in menslike sperm. Sperm is vir 1 uur by 37°C geïnkubeer in die teenwoordigheid van kumeenhidroperoksied en 0.1 mM [1- 14 C] d glukose en [3- 3 H] d-glukose. Die tempo's van pentosefosfaat en glikolitiese aktiwiteit is bepaal deur die vrystelling van 14 CO2 en 3H2O, onderskeidelik. Data word aangebied as die gemiddelde ± SD (n = 6). Verskillende boskrifte dui beduidende verskille aan (P ≤ 0,05) tussen kumeenhidroperoksiedkonsentrasies (eenrigting ANOVA plus Scheffe post-hoc-toets)

Effek van toenemende konsentrasies van kumeenhidroperoksied op die tempo van metabolisme deur (a) die pentosefosfaat en (b) die glikolitiese weë in menslike sperm. Sperm is vir 1 uur by 37 ° C geïnkubeer in die teenwoordigheid van kumeenhidroperoksied en 0,1 mM [1- 14 C] d glukose en [3- 3 H] d-glukose. Die tempo's van pentosefosfaat en glikolitiese aktiwiteit is bepaal deur die vrystelling van 14 CO2 en 3 H2O, onderskeidelik. Data word aangebied as die gemiddelde ± SD (n = 6). Verskillende boskrifte dui beduidende verskille aan (P ≤ 0,05) tussen kumeenhidroperoksiedkonsentrasies (eenrigting ANOVA plus Scheffe post-hoc-toets)

Byvoeging van 100 μM H2O2 verhoogde vloei deur die pentosefosfaatweg met meer as 100%, maar het geen effek op glikolitiese vloed gehad nie. Byvoeging van 50 μM H2O2 verhoogde pentosefosfaatwegaktiwiteit tot 'n kleiner en statisties onbeduidende mate, terwyl 500 μM glikolise aansienlik geïnhibeer het en pentosefosfaatwegvlakke verminder het, hoewel nie betekenisvol in vergelyking met kontrolewaardes nie (Fig. 2).

Effek van toenemende konsentrasies van H2O2 op die pentosefosfaatweg en glikolitiese vloed in menslike sperms. Sperm is in die teenwoordigheid van H geïnkubeer2O2 vir 1 uur by 37°C, en metaboliese tempo is gemeet soos beskryf vir Figuur 1. Data word aangebied as die gemiddelde + SD (n = 3). Verskillende boskrifte dui beduidende verskille aan (P ≤ 0,05) tussen H2O2 konsentrasies (eenrigting ANOVA plus Scheffe post-hoc toets)

Effek van toenemende konsentrasies van H2O2 op die pentosefosfaatweg en glikolitiese vloed in menslike sperm. Sperm is in die teenwoordigheid van H geïnkubeer2O2 vir 1 uur by 37 ° C, en metaboliese snelhede is gemeet soos beskryf in Figuur 1. Data word aangebied as die gemiddelde + SD (n = 3). Verskillende opskrifte dui op beduidende verskille (P ≤ 0,05) tussen H2O2 konsentrasies (eenrigting ANOVA plus Scheffe post-hoc toets)

Op 'n soortgelyke wyse is pentosefosfaatwegaktiwiteit verhoog deur die byvoeging van 1 mM xanthine en toenemende hoeveelhede XO (Figuur 3a). Dit was die gevolg van die gevolge van H2O2, omdat die effek geblokkeer is deur katalase (Fig. 3b), maar nie deur SOD nie (Fig. 3c). Xanthine het pentosefosfaatwegaktiwiteit bo die basale dosis verhoog, selfs in die afwesigheid van bygevoegde XO, wat impliseer dat sperm endogene XO-aktiwiteit het (Fig. 3a). Hierdie toename word ook toegeskryf aan H2O2omdat dit ook deur katalase geblokkeer is (Fig. 3b). Die 400 U/ml katalase het ook die basale tempo van pentosefosfaatwegvloei aansienlik verminder van 0,27 ± 0,02 nmol per 108 sperma per uur (gemiddelde ± SD, n = 5) in hierdie replikate tot 0,16 ± 0,02 nmol per 108 sperms per uur (P & lt 0,001, gepaar t-toets).

Stimulering van (a) die pentosefosfaatwegvloei in menslike sperm deur die superoksiedgenererende stelsel, xantien plus xantienoksidase, en die effekte van (b) katalase en (c) SOD. Sperm is vir 1 uur by 37°C geïnkubeer in die teenwoordigheid van 1 mM xanthine en toenemende konsentrasies van xanthine oksidase saam met katalase of SOD soos toepaslik. Vloei deur die pentosefosfaatbaan is gemeet soos beskryf in Figuur 1. Data word aangebied as die gemiddelde ± SD (n = 6). Verskillende opskrifte dui op beduidende verskille (P & lt 0,05) tussen xantienoksidase konsentrasies (eenrigting ANOVA plus Scheffe se post-hoc toets)

Stimulering van (a) die pentosefosfaatwegvloei in menslike sperms deur die superoksiedgenererende stelsel, xantien plus xantienoksidase, en die gevolge van (b) katalase en (c) SOD. Sperm is 1 uur by 37 ° C in die teenwoordigheid van 1 mM xantien en toenemende konsentrasies xantienoksidase saam met katalase of SOD geïnkubeer. Vloei deur die pentosefosfaatbaan is gemeet soos beskryf in Figuur 1. Data word aangebied as die gemiddelde ± SD (n = 6). Verskillende boskrifte dui beduidende verskille aan (P < 0.05) tussen xantienoksidase konsentrasies (eenrigting ANOVA plus Scheffe se post-hoc toets)

Om vas te stel of die glutathione peroxidase-glutathione reductase-pentose fosfaatwegstelsel op lipiedperoksidasie sou reageer, is sperm geïnkubeer met 200 μM askorbaat met of sonder 40 μM FeSO4. Ascorbaat alleen verhoog pentosefosfaatwegvloei van 0.32 ± 0.016 tot 0.47 ± 0.11 nmol per 108 sperma per uur (n = 5, P & lt 0.01, eenrigting ANOVA plus Scheffe-toets). Die toevoeging van FeSO4 het slegs 'n klein en statisties onbeduidende toename veroorsaak bo die wat deur askorbaat alleen geproduseer word, tot 0.50 ± .0.04 nmol per 10 8 sperm per uur. Die effek van askorbaat was nie afhanklik van die teenwoordigheid van endogene yster nie, want dit was onaangeraak deur die byvoeging van óf 0.4 mM EDTA óf 80 μM desferroksamien (data nie getoon nie).

Mercaptosuccinate is 'n remmer van glutathionperoksidase wat voorheen gebruik is om hierdie ensiem in sperms te belemmer. Tot ons verbasing het 40-320 μM merkaptosuksinaat geen effek gehad op óf die basale tempo van pentosefosfaatwegvloei óf die vloed in die teenwoordigheid van 10 μM kumeenhidroperoksied nie (Fig. 4a). Diëtielmaleaat, wat ons verwag het glutathion sou kompleks maak, het geen effek op die basale tempo van pentosefosfaatwegvloei gehad nie, maar het (gedeeltelik by 40 μM en heeltemal by 80 μM) die toename geproduseer deur 10 μM kumeenhidroperoksied geblokkeer (Fig. 4b).

Effek van (a) merkaptosuksinaat en (b) dietielmaleat op pentosefosfaatwegvloei van menslike sperma in die teenwoordigheid of afwesigheid van 10 μM kumeenhidroperoksied. Sperm is vir 1 uur by 37°C met wisselende konsentrasies merkaptosuksinaat of diëtielmaleaat geïnkubeer voor die byvoeging van 0.1 mM [1- 14 C] d-glukose en 10 μM kumeenhidroperoksied, waarna inkubasie vir 'n verdere uur voortgesit is. Vloei deur die pentosefosfaatbaan is gemeet soos beskryf in Figuur 1. Data word aangebied as die gemiddelde ± SD (n = 7 [a] en 9 [b]). Beduidende effek van kumeenhidroperoksied (gepaard t-toets) word soos volg aangedui: *P < 0,05, **P & lt 0,01, ***P & lt 0,001. Verskillende boskrifte verteenwoordig beduidende effekte (P & lt 0,05) van diëtielmaleat in die kumenhidroperoksiedbehandelde groep (eenrigting ANOVA plus Scheffe post-hoc-toets)

Uitwerking van (a) mercaptosuccinate en (b) dietielmaleat op pentosefosfaatwegvloei van menslike sperma in die teenwoordigheid of afwesigheid van 10 μM kumeenhidroperoksied. Sperm is vir 1 uur by 37°C met wisselende konsentrasies merkaptosuksinaat of diëtielmaleaat geïnkubeer voor die byvoeging van 0.1 mM [1- 14 C] d-glukose en 10 μM kumeenhidroperoksied, waarna inkubasie vir 'n verdere uur voortgesit is. Flux deur die pentosefosfaatbaan is gemeet soos beskryf vir Figuur 1. Data word aangebied as die gemiddelde ± SD (n = 7 [a] en 9 [b]). Beduidende effek van kumeenhidroperoksied (gepaar t-toets) word soos volg aangedui: *P < 0,05, **P & lt 0,01, ***P & lt 0,001. Verskillende opskrifte verteenwoordig beduidende effekte (P < 0,05) van diëtielmaleaat binne kumeenhidroperoksied-behandelde groep (eenrigting ANOVA plus Scheffe post-hoc toets)

Behandeling van sperm met 10 μg/ml van die glutathione-reduktase-inhibeerder BiCNU het konsekwent die vloed deur die pentosefosfaatweg verhoog van ongeveer 0.2 tot 0.3 nmol per 10 8 sperm per uur, terwyl 50–1000 μg/ml pentose-fosfaatweg-aktiwiteit afgeneem het. tot ongeveer 0,1 nmol per 108 sperms per uur (Fig. 5). Soos voorheen het 10 μM kumeenhidroperoksied pentosfosfaatwegvloei met meer as 50%verhoog. In die teenwoordigheid van 10 μM kumeenhidroperoksied, het 10 μg/ml BiCNU nie 'n verdere toename in die aktiwiteit van pentosefosfaat veroorsaak nie, maar 50-1000 μg/ml BiCNU het dit beduidend tot dieselfde waarde belemmer as waargeneem in die afwesigheid van kumeen hidroperoksied (Fig. 5).

Inhibisie van basale en kumeenhidroperoksied-gestimuleerde pentosefosfaat-wegvloei in menslike sperm deur BiCNU. Sperm is vir 1 uur by 37°C met wisselende konsentrasies BiCNU geïnkubeer, gevolg deur die byvoeging van 0.1 mM [1- 14 C] d-glukose en 10 μM kumeenhidroperoksied soos toepaslik. Die pentosefosfaatwegvloei is gedurende die daaropvolgende uur gemeet deur die vrystelling van 14 CO2 soos beskryf vir Figuur 1. Data word aangebied as die gemiddelde ± SD (n = 5). Beduidende effek van kumeenhidroperoksied (gepaar t-toets) word soos volg aangedui **P & lt 0,01. Verskillende opskrifte dui op beduidende verskille (P ≤ 0.05) tussen verskillende BiCNU-konsentrasies binne kumeenhidroperoksiedbehandelings (eenrigting ANOVA plus Scheffe post-hoc-toets)

Remming van basale en kumeenhidroperoksied-gestimuleerde pentosefosfaatwegvloei in menslike sperma deur BiCNU. Sperm is 1 uur by 37 ° C met verskillende konsentrasies BiCNU geïnkubeer, gevolg deur die byvoeging van 0,1 mM [1- 14 C] d -glukose en 10 μM kumeenhidroperoksied, soos toepaslik. Die pentosefosfaatwegvloei is gedurende die daaropvolgende uur gemeet deur die vrystelling van 14 CO2 soos beskryf vir Figuur 1. Data word aangebied as die gemiddelde ± SD (n = 5). Beduidende effek van kumeenhidroperoksied (gepaar t-toets) word soos volg aangedui **P & lt 0,01. Verskillende boskrifte dui beduidende verskille aan (P ≤ 0,05) tussen verskillende BiCNU-konsentrasies binne kumeenhidroperoksiedbehandelings (eenrigting ANOVA plus Scheffe post-hoc-toets)

In eksperimente met BiCNU is die beheersnelheid van vloed deur die glikolitiese weg (nmole [3- H] d -glukose omgeskakel na 3 H2O per 10 8 sperm per uur n = 5) was 25 ± 3.4. Dit is onaangeraak deur BiCNU by konsentrasies van 500 μg/ml of minder, maar dit het afgeneem tot 12 ± 1.9 met 1 mg/ml BiCNU (P & lt 0,05, eenrigting ANOVA plus Dunnett-toets). Die lewensvatbaarheid van die sperma gemeet aan die hipo-osmotiese sweltoets (HOST) toets gedra hom op dieselfde manier, met 500 μg/ml of minder BiCNU wat geen effek het nie, maar 1 mg/ml verminder die verhouding van lewensvatbare sperms met 10%.

Lipiedperoksidasie het toegeneem toe spermatozoa aan oksidatiewe spanning blootgestel is deur inkubasie met 1 mM xanthine plus 10 mU XO of met 100 μM H2O2, maar nie met 10 μM kumeenhidroperoksied nie (Fig. 6). Lipiedperoksidasie is ook verhoog na inhibisie van glutathioneduktase deur BiCNU (Fig. 7).

Invloed van oksidatiewe stres op lipiedperoksidasie in menslike sperm. Sperm is vir 1 uur by 37 ° C in BWW -medium geïnkubeer met óf 1 mM xantien plus 10 mU xantienoksidase, 100 μM H2O2, 10 μM kumeenhidroperoksied, of 'n ekwivalente volume BWW -medium (kontrole). Sperm is dan weer in HBSS gesuspendeer en vir 2 uur by 37 ° C geïnkubeer met 40 μM FeSO4 en 200 μM askorbaat, waarna malondialdehiedvrystelling gemeet is met behulp van 'n aangepaste tiobarbituriensuurbepaling. Data word aangebied as verhoudings om te beheer (gemiddelde + SD, n = 4). Beduidende verskille (P ≤ 0,05) van kontrole word deur verskillende superscripts aangedui (eenrigting ANOVA plus Dunnett post-hoc-toets)

Invloed van oksidatiewe stres op lipiedperoksidasie in menslike sperms. Sperm is vir 1 uur by 37 ° C in BWW -medium geïnkubeer met óf 1 mM xantien plus 10 mU xantienoksidase, 100 μM H2O2, 10 μM kumeenhidroperoksied, of 'n ekwivalente volume BWW-medium (kontrole). Sperm is dan hersuspendeer in HBSS en geïnkubeer vir 2 uur by 37°C met 40 μM FeSO4 en 200 μM askorbaat, waarna malondialdehiedvrystelling gemeet is met behulp van 'n aangepaste tiobarbituriensuurbepaling. Data word aangebied as verhoudings tot kontrole (gemiddeld + SD, n = 4). Beduidende verskille (P ≤ 0,05) van kontrole word deur verskillende superscripts aangedui (eenrigting ANOVA plus Dunnett post-hoc-toets)

Verhoogde lipiedperoksidasie in menslike sperma geïnkubeer met toenemende konsentrasies van BiCNU. Sperm is geïnkubeer in BWW-medium met verskillende konsentrasies BiCNU vir 2 uur by 37°C. Sperm is dan hersuspendeer in HBSS, en lipiedperoksidasie is gemeet soos beskryf vir Figuur 7. Data word aangebied as die gemiddelde ± SD (n = 4)

Verhoogde lipiedperoksidasie in menslike sperm geïnkubeer met toenemende konsentrasies BiCNU. Sperm is vir 2 uur by 37 ° C in BWW -medium met verskillende konsentrasies BiCNU geïnkubeer. Sperm is dan weer in HBSS gesuspendeer, en lipiedperoksidasie is gemeet soos beskryf in Figuur 7. Data word aangebied as die gemiddelde ± SD (n = 4)

Die belangrikheid van glutathione reduktase in die beskerming van spermfunksie is bestudeer deur die effek van BiCNU op spermmotiliteit onder 95% suurstof en onder 95% stikstof te meet. In die teenwoordigheid van 0–10 μg/ml BiCNU het beide die persentasie sperma wat beweeglik was en hul progressiewe snelheid (VSL) slegs effens gedaal tydens die 4-uur-inkubasie, ongeag die gasfase. In die teenwoordigheid van 50 μg/ml BiCNU het beide die persentasie beweeglike sperma en die VSL tussen 3 en 4 uur gedaal, en namate die BiCNU -konsentrasie toegeneem het tot 100 of 500 μg/ml, het die afname in beweeglikheid vroeër begin en meer geword ernstig. Met die hoër BiCNU -konsentrasies (100 en 500 μg/ml), was die afname merkbaar groter in die inkubasies onder 95% suurstof as in dié onder 95% stikstof (Fig. 8, a – d). Die effek van suurstof kon duideliker gesien word deur die verhouding tussen beweeglikheid onder suurstof en beweeglikheid onder stikstof te ondersoek. Beide die persentasie beweeglike sperms en die VSL het duidelik aansienlik vinniger en ernstiger afgeneem onder 95% suurstof in die teenwoordigheid van 100 en 500 μg/ml BiCNU, en vir die persentasie beweeglike sperms kon hierdie effek ook gesien word met 50 μg /ml (Figuur 8, e en f). Breedweg soortgelyke veranderinge is gesien vir die persentasie vinnig beweeglike (gemiddelde padsnelheid [VAP], >25 μm/sek) sperm, kromlynige snelheid en VAP (data nie getoon nie).

Die effek van 0–500 μg/ml BiCNU op (a en d) die persentasie van geleidelik beweeglik, (b en e) hul reguitlynsnelheid (VSL), en (c en f) hul laterale kopverplasing (ALH) wanneer dit onder (a – c) 95% N2/5% CO2 of (d – f) 95% O2/5% CO2 en die verhoudings van (g) die persentasie beweeglike sperms, (h) VSL, en (f) ALH onder 95%O2 oor die ooreenstemmende waarde onder 95% N2. Sperm is in BWW -medium gesuspendeer en by 37 ° C in verseëlde buise onder die toepaslike gasfase geïnkubeer. Afsonderlike buise is vir elke tydstip voorberei. Op die toegelate tyd is buise oopgemaak en 'n klein hoeveelheid sperms is na 'n "mikrosel" (diepte, 20 mikrometer) oorgedra vir motiliteitsbeoordeling deur middel van rekenaargesteunde sperma-analise. 'N Aansienlik groter effek van BiCNU onder O2 as onder N2 word soos volg aangedui: *P < 0,05, **P & lt 0,01, ***P & lt 0.001 (herhaalde metings ANOVA)

Die effek van 0–500 μg/ml BiCNU op (a en d) die persentasie van progressief beweeglik, (b en e) hul reguitlynsnelheid (VSL), en (c en f) hul laterale kopverplasing (ALH) wanneer geïnkubeer onder (a – c) 95% N2/5% CO2 of (d-f) 95% O2/5% CO2 en die verhoudings van (g) die persentasie beweeglike sperm, (h) VSL, en (f) ALH onder 95%O2 oor die ooreenstemmende waarde onder 95% N2. Sperm is in BWW -medium gesuspendeer en by 37 ° C in verseëlde buise onder die toepaslike gasfase geïnkubeer. Afsonderlike buise is vir elke tydpunt voorberei. Op die toegelate tyd is buise oopgemaak en 'n klein volume sperm is oorgedra na 'n "Mikrosel" (diepte, 20 μm) vir beweeglikheidsbepaling deur rekenaargesteunde semenanalise. 'N Aansienlik groter effek van BiCNU onder O2 as onder N2 word soos volg aangedui: *P < 0,05, **P & lt 0,01, ***P < 0,001 (herhaalde maatreëls ANOVA)


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In: FEBS Letters, Vol. 440, nr. 3, 04.12.1998, p. 430-433.

Navorsingsuitset: Bydrae tot tydskrif ›Artikel› ewekniebeoordeling

T1 - Onderdrukking van ensieme van die pentosefosfaatweg deur glukose in splitsingsgis

N2 - Ons ondersoek hier die effek van koolstofbronne op die sintese van die shuntweg-ensieme in die splytingsgis Schizosaccharomyces pombe wat op 'n mengsel van etanol en gliserol groei. δ-Gluconolactone veroorsaak feitlik elkeen van hierdie ensieme. Glukose daarteenoor is geneig om die sintese van die meerderheid daarvan te verswak. RNA-analise bevestig dat hul induksie en onderdrukking veranderinge in die vlakke van hul transkripsies weerspieël. Kopiereg (C) 1998 Federasie van Europese Biochemiese Verenigings.

AB - Ons ondersoek hier die effek van koolstofbronne op die sintese van die shuntweg -ensieme in die splitsingsgis Schizosaccharomyces pombe wat groei op 'n mengsel van etanol en gliserol. δ-Gluconolactone veroorsaak feitlik elkeen van hierdie ensieme. Glukose daarteenoor is geneig om die sintese van die meerderheid daarvan te verswak. RNA -analise bevestig dat hul induksie en onderdrukking veranderinge in die vlakke van hul transkripsies weerspieël. Kopiereg (C) 1998 Federasie van Europese biochemiese verenigings.


Bespreking

In hierdie studie het ons ondersoek hoe die Mφ vermoë om te beheer Tc infeksie is gedemp en het 'n metaboliese benadering gevolg om die trypanocidale funksie van M φ's te verbeter. Hiervoor het ons primêre en gekweekte Mφs gebruik tesame met genetiese en chemiese uitputting van PPARs, metaboliet-profilering gevolg deur aanvulling van kritieke metaboliete en chemiese en RNAi-inhibisie van sleutelmetaboliese ensieme om die Mφ-reaksie op Tc. Ons data het getoon dat M φ's besmet is met Tc en veroorsaak dit 'n kragtige, inflammatoriese sitokienrespons, maar dit het nie effektiewe ROS- en GEEN reaksies teen die parasiet nie. Ons het getoon dat dit te wyte is aan M φ's wat steeds 'n PPAR-α-afhanklike, Krebs-siklus-gekoppelde oksidatiewe metabolisme handhaaf wat geen effek op inflammatoriese sitokienrespons het nie, maar slegs 'n gedeeltelike vlak van NOX2/iNOS-aktivering moontlik maak Tc infeksie. IFN-γ-behandeling het die M φ's en die behoefte om Krebs-gesteunde Krebs-siklus te gebruik, gelei tot 'n volledige metaboliese afsluiting van die oksidatiewe metabolisme en 'n verbetering van die glikolitiese bron van energiebeskikbaarheid in besmette M φ's. Ironies genoeg is die opname en metabolisme van glukose na PPP herlei, en die aktiwiteit van PGD, wat Ru5P en NADPH produseer, was noodsaaklik vir die opwekking van kragtige ROS en GEEN reaksie by besmette M φ's. Inhibering van PGD het gelei tot verminderde ROS/NO -vlakke, toename in parasietreplikasie en vroeëre vrystelling van trypomastigote uit besmette M φ's. Sover ons weet, is dit die eerste studie wat 'n gedetailleerde oorsig gee van die metaboliese regulering van die M φ -reaksie op 'n intrasellulêre patogeen, T. cruzi. Ons stel voor dat chemiese analoë wat die glukose–pentosefosfaat-shunt verbeter voordelig sal wees in die beheer van vroeë parasietreplisering en verspreiding in die besmette gasheer.

Die TLR -familie van aangebore immuunreseptore (TLR1 –TLR10) herken 'n verskeidenheid patogeenligande en begin twee hoofweë. Die MyD88-afhanklike pad word deur alle TLR's behalwe deur TLR3 gebruik vir die aktivering van NF-㮫 en aktivatorproteïen-1 (AP-1) transkripsiefaktore, terwyl die IFN-β-afhanklike pad geïnisieer word deur TLRs 3 en 4 aktiveer die TIR-domeinbevattende adapterproteïen en tipe I IFN-antwoorde. T. cruzi en Tc antigene (bv. GPI-geankerde mucins, cruzipain) word getoon om TLR2 en TLR4 te betrek, en Tc DNS word deur TLR9 herken om pro-inflammatoriese sitokienreaksie in Mφs te veroorsaak (22). Ongelukkig het die Tc geïnduseerde sitokienreaksie blyk onvoldoende om parasiete te beheer. Die oorheersing van pro-inflammatoriese sitokiene, IFN-γ, TNF-α, IL-17, met TLR2 en TLR4 betrokkenheid is patologies vir die gasheer, en word voorgestel om betrokke te wees by die voorstelling van 'n hartvorm van siekte by besmette mense (23). TLR2 en TLR4 word ook voorgestel om betrokke te wees by die vervaardiging van ROS en NO (24), maar in die konteks van Tc infeksie, TLR2/TLR4-aktivering blyk nie voldoende te wees om kragtige ROS/NO-reaksie te veroorsaak om die intrasellulêre parasiet dood te maak nie (25). Ander het voorgestel dat dit nie die onvermoë van M φ's is om 'n ROS/NO-reaksie op te stel nie, maar die uitgebreide antioksidantstelsel van trypanothione-afhanklike tryparedoksienperoksidases ontwrig die ROS/NO (12, 26). Ons studie dui daarop dat dit moontlik nie die enigste oorsaak is van 'n sub-par ROS/NO-reaksie nie. Supplementing with IFN-γ during infection was sufficient to activate the mφ expression and activation of iNOS and NOX2, and production of NO and ROS, respectively. How ROS influences parasite control in Mφs have been controversial, including that low levels of supplied ROS or gp91phox knockout aids in parasite replication, while high levels of ROS are toxic to T. cruzi (27). Further, Paiva et al have suggested that oxidative stress fuels T. cruzi infection in mice (28) while studies from our laboratory indicate that inhibition of the antioxidant mechanisms resulted in increased tissue pathology in chagasic murine myocardium (29). These studies illuminate the complex fine gauging of ROS levels necessary for effective Tc killing by Mφs. Further studies will be required to identify how IFN-γ complements the Tc-generated stimuli in enhancing the ROS/NO response above the threshold for parasite killing. The two pathways that deserve immediate attention include the interaction of the atypical PKC ζ and TLR2 in the lipid rafts of the plasma membrane and the TLR4-MyD88-IL-1 receptor-associated kinase 4 signaling pathway that activate the p38 MAPK and protein kinase B pathways, which can initiate the phosphorylation of p47 phox and subsequent activation of NOX2 and ROS production in Mφs (30, 31).

How energy metabolism is reconfigured to support Mφ activation and effector function has not been fully studied. PPARs (α, γ, and δ isoforms) are ligand-activated transcription factors that regulate nearly every facet of fatty acid metabolism. Recent studies have established a role for PPAR-γ and -δ in the regulation of Mφ lipid metabolism and inflammation. Several groups have noted upregulation of PPAR-γ in murine and human Mφs, and initial studies suggested that PPAR-γ attenuates the pro-inflammatory Mφ response (19). Agonism of PPAR-γ coupled the uptake of oxidized low density lipoprotein to cholesterol efflux via induction of liver X receptor-α-mediated transcriptional cascade and the cholesterol efflux pump Abca1, and was beneficial in providing the atheroprotective effects in diabetes (32). Others have suggested that PPAR-δ-dependent shift toward oxidative metabolism is accompanied by an influx of fatty acids, and PPAR-δ-dependent surge in monounsaturated fatty acids synergize with IL-4 to enhance the alternative gene expression signature (33). Macrophage-specific knockdown of PPAR-γ resulted in a loss of alternatively activated Mφs in tissues and increased susceptibility to diet induced obesity, insulin resistance, and glucose intolerance in mice (34). The role of PPAR-α in Mφs is comparatively less studied. In 'n T. cruzi infection mouse model, PPAR-α mRNA expression has been shown to be enhanced in peritoneal Mφs isolated from mice at 6 days post-infection (20). Our study provides evidence that PPAR-α protein level also increases in murine Mφs by Tc-generated stimulus. Interestingly, genetic and chemical ablation of PPAR-α activity had no effect on the inflammatory cytokine response of infected Mφs however, PPAR-α appeared to stimulate the ROS and NO production, at least partially, in response to initial infection. Inhibition of PPAR-α decreased the oxidative metabolism and the NO and ROS response in infected Mφs. A similar suppression of NO and ROS was observed with the inhibition of pyruvate transport to the mitochondria early in pro-inflammatory activation, which overall suggested that PPAR-α-regulated mitochondrial metabolism may be involved in the early events that lead to ROS and NO production by infected Mφs. Inhibiting mitochondrial pyruvate transport had been shown to suppress iNOS gene transcription in LPS-activated Mφs (35). A broken Krebs cycle results in accumulation of metabolites, e.g., succinate, which signaled transcriptional activation of inflammatory response in LPS-stimulated Mφs (21). We also observed a moderate increase in Krebs cycle metabolites including succinate in infected Mφs. Alternatively, a functional mitochondrial Krebs cycle could support the production of oxidative compounds as it has two enzymes that produce NADPH, which is utilized by NOX2 and iNOS for synthesizing ROS and NO, respectively. Further studies will be required to delineate the comparative role of PPAR-α in providing transcriptional and metabolic signals for regulating the NOX2/iNOS activation in Mφs. Regardless, PPAR-α inhibition was not sufficient to arrest parasite replication in Mφs.

Recent studies have described an increase in glycolysis-dependent lactate formation and activation of PPP in Mφs after phagocytosis (13), and that inhibition of sedoheptulose kinase (CARKL), which resulted in accumulation of metabolites in the PPP and a decline in Krebs cycle metabolites, enhanced the pro-inflammatory cytokine response in LPS-activated Mφs (36). Others showed that HIF1α-dependent transcriptional programming is responsible for heightening glycolysis in Mφs (14), and GLUT1-mediated glucose uptake drives a pro-inflammatory phenotype (37). In this study, we provide evidence that first few steps where glycolysis and PPP are linked, primarily support ROS and NO production in inflammatory Mφs. Our data show that in all instances when glucose availability was limited, achieved by inhibition of GLUT1, removal of glucose, or replacement of glucose with fructose as a carbon source, the levels of cytokine release were not largely altered while ROS and NO responses were abolished in Tc- and LPS-stimulated Mφs. IL-6 release were initially delayed with the inhibition of pyruvate transport or GLUT1, which may suggest an early transcription factor of IL-6 is influenced by metabolic signaling such as that demonstrated by cyclic adenosine monophosphate levels (38). Glutamine, which can replenish the Krebs cycle through its conversion to glutamate and α-ketoglutarate, was also insufficient in the absence of glucose to support cell viability and the ROS/NO response of activated Mφs. The increase in abundance of glucose-6-P/fructose-6-P and glycerol-3-P metabolites of glycolysis pathway and Ru5P of the PPP that reversibly fuel each other provided the first indication that activation of potent ROS/NO response in Mφs requires a coordinated regulation of glycolysis to PPP, instead of glycolytic formation of pyruvate or lactate. This was also evidenced by the findings that ROS/NO response was abolished by inhibition of PGD (produces Ru5P and NADPH) in infected Mφs. Future studies will be required to delineate if glycolytic-pentose phosphate shunt simply provides the NADPH substrate, or it provides metabolic signaling at transcriptional, translational, or posttranslational levels for NOX2 and iNOS activation in pro-inflammatory Mφs. Yet, we surmise that activation of glycolytic-pentose phosphate shunt will be beneficial in enhancing the Mφs’ ability to achieve early clearance of intracellular parasites.

In summary, the present study shows that early inhibition of mitochondrial metabolism may be detrimental for ROS and NO generation, glycolysis and PPP are important for ROS and NO generation at the metabolite level, and Tc infection may program the metabolism of host Mφs differentially at the pentose phosphate shunt compared to pro-inflammatory Mφs. Based on these findings, we extend our understanding of how the synthesis or release of ROS and NO compounds are controlled by metabolism, which may be further studied for potential translational purposes.


Pentose phosphate pathway

Pentose phosphate pathway
The penthose phosphate pathway (also known as the Hexose Monophosphate Shunt) is a process that serves to generate NADPH and the synthesis of pentose (5-carbon) sugars. There are two distinct phases in the pathway.

(= pentose phosphate pathway)
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If you know of any terms that have been omitted from this glossary that you feel would be useful to include, please send details to the Editorial Office at GenScript.

Die Pentose Phosphate Pathway
Glycolysis & the Citric Acid Cycle
Gluconeogenesis: Definition, Steps & Pathway .

"Non-enzymatic glycolysis and

-like reactions in a plausible Archean ocean". Mol Syst Biol. 10: 725. doi:10.1002/msb.20145228. PMC 4023395. PMID 24771084.
^ Kim BH, Gadd GM. (2011) Bacterial Physiology and Metabolism, 3rd edition.
^ a b Lane, A. N. Fan, T. W. -M. Higashi, R.

An upregulation of mitogenic pathways, whether caused by mutant genes or overabundance of growth factors, would amplify the glycolytic flux feeding the glycosyl pathway, the PPP (

), the serine pathway, and the one carbon metabolism, which drive biomass production, including nucleotides, .

The first pathway, present in many bacteria and few fungi, involves xylose isomerase which converts d-xylose to xylulose and phosphorylation of xylulose by xylulokinase followed by its entry to

(Harhangi et al, 2003 Lawlis et al, 1984 Lokman et al, 1991 Rygus et al, 1991, Scheler et al, .

Intermediate products of glycolysis, the citric acid cycle, and the

can be used to make all twenty amino acids, and most bacteria and plants possess all the necessary enzymes to synthesize them. Humans and other mammals, however, can synthesize only half of them.

glucose-6-phosphate (G6P) Glucose sugar phosphorylated on carbon 6. Represents the first step of glycolysis and the

. Most of the glucose in a cell is phosphorylated in this way upon entry.
Online Biology Dictionary (GLUTA-) .

D is correct. In muscle cells, glucose-1-phosphate is converted to glucose-6-phosphate by phosphoglucomutase, after which it may enter the glycolytic or

s. In liver cells, glucose-6-phosphate is converted to glucose by glucose-6-phosphatase and released into the bloodstream.
Verwysings.


Supplement 1

19.5.6.1 Furfural and derivatives

The acid-catalyzed hydrolysis of polymeric pentoses all the way down to their corresponding monosaccharides (aldopentoses) followed by acid-catalyzed dehydration 139 leads to the formation of 2-furancarbaldehyde (furfural) ( 41 ). D-Xylose gives the highest yields: Scheme 13 illustrates the accepted mechanism of this triple dehydration.

Rhamnose, formed from the corresponding methylated units in hemicelluloses, yields concurrently small amounts of 5-methyl-2-carbaldehyde (methylfurfurnal) ( 42 ), which is therefore a typical ‘impurity’ in the manufacture of furfural. If needed, the separation of these two homologues is readily achieved by fractional distillation.

This process was industrialized more than 50 years ago and is today applied to a large variety of pentosans-rich raw materials, mostly agricultural wastes such as corn cobs, rice hulls, sugar-cane bagasse, olive residues and cotton seeds, but also wood and by-products of paper mills. 140 It can be envisaged that the newer technologies of biomass refining, stream explosion and organosolv processes for example, will select this chemical post-treatment as one of the major alternatives for the rational use of the hemicelluloses arising from them. The yearly production of furfural amounts to about 200000 tons. Most of it is catalytically reduced to fufuryl alchohol ( 43a ) which constitutes therefore the most important industrial chemical of the furan series presently available on the market. 141 This is due to the usefulness of fufuryl alcohol as monomer in the preparation of various resinous materials. 141 However, many other monomers can be prepared from fufural and thus be the source of new polymers. 2,141,142,144

The catalytic decarbonylation of ( 41 ) en ( 42 ) is the standard procedure for the synthesis of furan ( 44 ) and 2-methylfuran ( 45 ), both available industrially. Furan is one of the two industrial sources of tetrahydrofuran ( 46 ), the other being 1,4-butanediol. Both furan and tetrahydrofuran are monomers, but for very different materials, as discussed below.

Certain hexoses used as such, or formed in the hydrolysis of polysaccharides such as starch or inulin, can be exploited in a manner similar to that described for pentoses and their acid-catalyzed dehydration 139,145–147 affords then 5-hydroxymethyl-2-furancarbaldehyde (hydroxymethyl furfural) ( 47 ) or 5-chloromethyl-2-furancarbaldehyde, the latter being the specific product arising when HCL is used as catalyst. The mechanism of formation of ( 47 ) from fructose 145 is shown in Scheme 14 .

Compound ( 47 ) is not an industrial commodity as yet, but a pilot plant based on an original aqueous process using a chromatographic separation procedure has been operating for a few years. 148 Other processes are being actively studied 147 with the aim of reaching a viable industrial realization. The use of ( 47 ) as precursor to furanic monomers 143,144 is the second object of this section.

Glucose can be conveniently converted into furanic tetrols by condensation with dicarbonylic compounds in the presence in the presence of mild Lewis acids such as calcium chloride, 149 as shown by equation (7) .

The interest of this process is that starting from sucrose and proceeding to its hydrolysis into fructose and glucose, one can envisage the use of the latter for the preparation of furanic tetraols and take advantage of the selectivity of reaction (7) 149 to recuperate the untouched fructose for other utilizations, bv. the preparation of ( 47 ). Reaction (7) also applies to certain pentoses and then gives furanic triols. All these polyolos constitute interesting monomers for the synthesis of polyurethanes.

The monomers arising from ( 41 ) en ( 42 ) can be first-or second-generation derivatives, as sketched in the general pattern given in Scheme 15 .

All the above monomers generate in principle macromolecular structures in which the furan ring is pendant to the chain and not part of it. This is so only if no side reactions occur which implicate the heterocycle. It will be shown that such anomalies do take place in some systems.

2-Alkenylfurans ( 48 ) are among the oldest furanic monomers studied. Their synthesis follow three alternative routes: (i) the classical condensation of the furanic aldehyde with malonic acid to give the 2-furanacrylic acids, which are then decarboxylated at relatively high temperature 150 (ii) the Witting reaction between the same aldehydes and phosphonium salts which has been optimized with an original application of phase-transfer catalysis 151 (iii) the Grignard reaction applied to both furanic aldehydes and ketones to produce the respective alcohols, followed by their dehydration 152 and (iv) the lithiation of furan ( 44 ) and 2-methylfuran ( 45 ) followed by the addition of acetaldehyde or acetone to give the secondary or tertiary alcohols 153 which are dehydrated as in (iii). Whereas methods (i) and (ii) provides ways to prepare the vinyl derivatives (48a) en (48b) only, methods (iii) and (iv) apply to all four alkenylfurans ( 48 ). However, method (ii) is by far the best in terms of ease of application, economy and yields. 154

Another well-known family of monomers is that of 2-furfurylidene ketones ( 49 ). Their preparation involves a simple aldol-type condensation of furanic aldehydes with ketones or aldehydes in a basic (aqueous) medium. The specific reaction of ( 41 ) with acetone to give the parent compound ( 49a ) has been thoroughly investigated and optimized. 155

The 2-furyloxiranes ( 50 ) on the other hand, are a more recent acquisition. They are prepared by the reaction of furanic aldehydes with triphenylmethylphosphonium bromide, with a basic solid providing phase-transfer catalysis. A through investigation of these synthesis 156 has defined the parameters allowing a near-quantitative yield under mild conditions and short reaction times.

2-Furyl ethenyl ketones are best prepared from furanic ketones. 157,158

Furfuryl alchohol ( 43a ) and its 5-methyl homologue ( 43b ), prepared by the reduction of ( 42 ), are precursors to other furanic monomers. Their esterification with acrylic and methacrylic acid chlorides or anhydrides give the corresponding furfuryl derivatives ( 51 ) in a straightforward manner. Another synthesis has also been reported for these monomers. The vinyl exchange reaction of ( 43 ) with, bv., isobutyl vinyl ether provides a route to furfuryl vinyl ethers ( 52 ). 159

The 2-furoic acids ( 53 ), prepared by oxidation of ( 41 ), en ( 42 ) are also intermediates for the synthesis of furanic monomers. Their chlorides are readily transformed into azides which in turn yield the corresponding isocyanates ( 54 ) by the Curtius reaction. 160 Alternatively, vinyl exchange reactions of these acids with, bv., vinyl acetate give the corresponding vinyl furoates ( 55 ). 161

The 2-furfurylamines ( 56 ), of which ( 56a ) is a commercial derivative of furfural, provide another set of monomers, nl. 2-furfurylisocyanates ( 57 ), 160 through their reaction with phosgene, or, better still, with bis(trichloromethyl) carbonate, known as triphosgene.

Whereas all the above reactions provide monomers which are suited for chain polymerization reactions, esters of ( 53a ) en ( 56a ) can also be used as precursors to difuranic difunctional dimonomers for polycondensation reactions. The well-known acid-catalyzed condensation of furan derivatives with aldehydes or ketones shown in equation (8) is applied successfully to this specific context. 124,161

The diesters can be used as such in polytransesterification reactions, or transformed into diacids, diacid chlorides, their nitriles and eventually their furanic diisocyanates. The diamine salts are also a source of diisocyanates by phosengenation, but this time one is dealing with furfuryl diisocyanates.


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Microbial Metabolism☆

Alternative Catabolic Pathways

Organisms lacking phosphofructokinase, the defining enzyme of the EMP pathway, must use an alternative carbohydrate pathway to form key intermediates for biosynthesis and substrate level phosphorylation reactions. The following are the most commonly occurring alternative pathways:

Hexose Monophosphate Pathway and Variations

Any one of a variety of forms of this pathway is used by different groups of bacteria for biosynthetic purposes (to produce ribose 5-phosphate for the biosynthesis of nucleic acids) or as a fermentation pathway. In the initial steps of the pathway, reactions of the oxidative portion of the pentose phosphate pathway (see above) result in the oxidative decarboxylation of glucose-6-phosphate to a pentose monophosphate product. The definitive enzyme of the pathway is 6-phosphogluconate dehydrogenase. Subsequent cleavage of the pentose phosphate typically produces glyceraldehyde 3-phosphate and acetate or acetyl phosphate (depending on the enzyme system). The net yield of ATP for this pathway is typically only 1 ATP per glucose molecule. However, some bacteria use portions of these reactions, along with the EMP reactions, to derive up to 2.5 moles of ATP per mole glucose.

Entner–Doudoroff Pathway (ED)

This pathway is used by organisms such as Pseudomonas en Neisseria in place of the EMP for growth on glucose. It is also co-existent with the EMP in some intestinal bacteria and plays a major role in growth on sugar acids, which are found on host cell surface molecules in the gastrointestinal tract. The yield of ATP for this pathway is 1 ATP per glucose molecule. Two versions of the pathway are found – one cleaves a monophosphorylated hexose derivative, whereas the other cleaves a nonphosphorylated substrate. The unique enzyme of this pathway is 6-phosphogluconate dehydratase (EDD).