Chapter24 PPP.ppt

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1、Chapter24PhosphatePentosePathway,(PPP),OverviewofPPPAllPPPreactionsPhysiologicalfunctionsofPPPRegulationofPPP,Outline,PentosePhosphatePathway,Aka:Pentoseshunt,HexosemonophosphateshuntandPhosphogluconatepathwayItoccursinthecytosol.Twooxidativeprocessesfollowedbyfivenon-oxidativestepsOperatesactiveint

2、hecytosolofliverandadiposecells,CellsneedaconstantsupplyofenergyNADH,NADPHandATPATP-energycurrencyNADPH-reducingpowerGlucose-NADH-ATPGlucose-NADPH-biosynthesis(reductive)PPPProvidesNADPHandribose-5-P,PentosePhosphatePathway,AllthePPPreactions,Glucose-6-PDehydrogenase:Irreversible1ststep-highlyregula

3、ted(inhibitedbyNADPH)Gluconolactonase:Uncatalyzedreactionhappenstoo6-PhosphogluconateDehydrogenase:Anoxidativedecarboxylation,OxidativePhase,Regulatoryenzyme,TheenzymeishighlyspecificforNADP+;theKmforNAD+is1000greaterthanforNADP+.,Step1:DehydrogenationofGlucose-6-phosphate,Step2:HydrolysisofLactone,

4、Step3:Dehydrogenationof6-phosphogluconate,Transketolase:transferoftwo-carbonunitsTransaldolase:transfersathree-carbonunit,TheNonoxidativePhase,Step4andStep5:Conversionofribulose5-phosphatetoxylulose5-phosphateorribose5-phosphate,VariationsonthePPP,Moreribose-5-PthanNADPHisneededBothribose-5-PandNADP

5、HareneededMoreNADPHthanribose-5-PisneededNADPHandATPareneeded,butribose-5-Pisnot,Rapidlydividingcellsrequiremoreribose5-phosphatethanNADPH,TheneedforNADPHandribose5-phosphateisbalanced,MoreNADPHisneededthanribose5-phosphate;Fattyacidsynthesisinadiposecells,ThecellneedsbothNADPHandATP,TheUseofNADPH,B

6、iosynthesisfattyacidsphotosynthesisDNAsynthesisRedoxregulationofcellularprocessescontrolofcellularredoxstatedisulfidebondformationantioxidantdefense,GlutathioneandNADPH,GlutathionePeroxidasecatalyzesdegradationoforganichydroperoxidesbyreduction,astwoglutathionemolecules(representedasGSH)areoxidizedt

7、oadisulfide.2GSH+ROOHGSSG+ROH+H2OGlutathionePeroxidaseusesthetraceelementseleniumasfunctionalgroup.Theenzymesprimarystructureincludesananalogofcysteine,selenocysteine,withSereplacingS.RegenerationofreducedglutathionerequiresNADPHproducedinthePentosePhosphatePathway.GlutathioneReductasecatalyzes:GSSG

8、+NADPH+H+2GSH+NADP+GeneticdeficiencyofGlucose-6-PDehydrogenasecanleadtohemolyticanemia,duetoinadequateNADPHwithinredbloodcells.EffectofpartialdeficiencyofGlucose-6-PDehydrogenaseisexacerbatedbysubstancesthatleadtoincreasedproductionofperoxides(e.g.,theantimalarialprimaquine,oracompoundinfavabeans).,Killpathogens,