CYTOSOLPLASTIDStorage,StarchphloemtransportSucroseGlycolysisPentosePentosephosphatephosphatepathwaypathwayHexose-pHexose-pPentose-pPentose-pTriose-PTriose-PCO2NADPHCO2NADPHPhotosynthesisOrganicacidsStorageATPNADHATP福MITOCHONDRIONNADHCitricOxidativeFADH2acidphosphorylationcycleCO2O2LipidbreakdownFigure 4-1
Figure 4-1
(A)InitialphaseofglycolysisSubstratesfromdifferentsourcesarechanneiedintotriosephosphate.oreachmoleculeofsucrosethatismetabolizedfourmoleculesoftriosephosphateareformed.TheSucroseCYTOSOLprocessrequiresaninputofuptoaATpUDPPLASTIDinvertaseGlycolysisSucrose svnthaseStarchStarch+phosphorytaseAmylaseGlucoseFructoseUDP-GlucosePHPPUDP-GiucaseATPATPGlucose-1-pGlucosepyrophosphorylaseHexokinaseHexokinaseUTPATPPhosphoGlucose-1-pADPCADPVGlucosegluco.ADPYtphosphoglucomutasekinasemutaseGlucose-6-pFructose-6-1-Glucose-6-pGlucose-6-PHexoseAMYLOPLASTSHexoseHexosephosphatesphosphatephosphatesomeraseisomerasePPATPATp-dependentpp-dependentphosphofructokinasephosphofructokinaseCADPPFructose-1,6-bisphosphateAldolaseCHLOROPLASTSTrioseTrioseGlyceraldehyde-DihydroxyacetonephosphatesTriosephosphatephosphates3-phosphateohoshatesomerase?NAD+Eneray-conservingphaseofgiycoysisGiyceraldehyde.NADHTriose phosphateisconvertedtopyruvate3-phosphatedehydrogenaseNADisreduced toNADHby giyceraldehyde-1,3-Bisphosphoglycerate-phosphatedehydrogenase.ATpissynthesizedinthereactionscatalyzedbyADEDosphoglyceratekinaseandpyruvateDphosphogiycerate kinasekinase.Anaiternativeendproduct,ATPphosphoenolpyruvate,canbeconvertedtomalateforrnitochondrialoxidation;NADH3-Phosphoglyceratecan bereoxidized during fermentationbyeither lactatedehydrogenase oralcoholphosphoglycerate mutasedehydrogenase.2-PhosphoglycerateEnolaseHCO.H2OPEp.carboxylasephosphoenolpyruvateOxaloacetate?CADPNADHPMalatepyruvatekinasedehydrogenaseNAD+XATPPyruvateMalateNADHLactatedehydrogenasecONAD+LactateTOPyruvateFigure 4-2MITOCHONDRIONdecarboxylaseAcetaldehydeNADHAlcoholdehydrogenaseNAD?FermentationEthanolroctions
Figure 4-2
(A)(B)IntermembranespaceOutermembraneInnermembraneADPATP-HSSMatrixFIGURE1.15(A)Diagrammaticrepresentationofamitochondrion,including thelocation ofthe H+-ATPasesinvolvedinATPsynthesis ontheinnermembraneFigure 4-3(B)Anelectronmicrographofmitochondria fromaleaf cellofBermudagrass,Cynodondactylon.(26,oo0x)(PhotobyS.E.Frederick,courtesyofE.H.Newcomb.)
Figure 4-3
0OnMalicenzymePyruvateCH.decarboxylatesmalatetoOHpyruvateand enablesplantmitochondriatoCoANADOxidize malate,PyruvateNADHdehydrogenase-CO2OAcetyi-CoACHCOAoONADHCitrateONADH-synthaseHMalateCHCOACH2Malicdehydrogenase儿HenzymeoOHCO2NAD+OxaloacetateCitrateNAD+OHAconitaseCHO0OHMalateAFumaraseCH.OHOCitricOCH2IsocitrateIUacid-FumarateOcycleOHOTOFADHZNADSuccinatedehydrogenaseIsocitratedehydrogenaseFADNADHoSuccinate2-OxoglutarateCO2HHOHC-OCHCH2COA0OoCOAATPSuccinyl-CoAADPSuccinyl-CoA synthetaseOONADH,OCHCHZ-OxoglutaratedehydrogenaseOnemoleculeofATpissynthesizedbyasubstrateCOANADHcO.levelphosphorylationduring thereactioncatalyzedbysuccinyl-CoAsynthetase.Figure 4-4FiGURE11.6Reactions and enzymes of theplant citric acid cycle.Pyruvateiscompletely oxidized tothreemoleculesof COa.Theelectrons released duringthese oxidations areused toreducefourmolecules ofNAD+toNADHandonemoleculeofFADtoFADHat
Figure 4-4
Theoribulose-5-phosphatesNADpHisaeneratedinthefirstconverted to the glycolytictworeactionsofthepathwayintermediatesfructose-owhere alucose-6-phosphateisphosphate anctglyceraldehyde-3.oxidizedtoribulose-siphosphatephosphatthrauhaseriesotThesereactionsarossentiallymetabolelnterconversions.Thoserroversiiereactions are freeiyroversible,CHCRibulose--phosphateSHpentosophosphatepentosephosphateHMCepimerasieisomeraseHOH--Glucose-G-phosphateCHOHCHNADPEGlucose-e--OHCOHCphosphateNADPHdehydrogenaseHOCHHCOHCOOHHCOHHCOHHCOHCHO-DCHOHOCHXylulose-s-phosphateRibose-s-phosphate.HCOHTransketolaseHCOHCH.OH?CH,OCHOOG-phosphogluconateNADPEHCOHHOCHco.NADPHCHao-PHCOHGtuconate-6.phosphateGiyceraldahyde-CHOHHCOHdehydrogenase-phosphateCHCOHHCOHCHOPSedoheptuloseHCOH7-phosphateCH,OPRibulose-S-phosphateTransaldolaseCHOCH,OHHCOHOHCOHHOCHHoxosephosphateHCOHCHOPisomneraseErythroseHCOHa-phosphatePranskotoiaseCHO-Pructosie-G-phosphate?CHOHCOHCH.OPGtyceraldehyde-Figure 4-53-phosphateReactionsoftheoxidativepontosephosphateFIGURE11.4Ephosphate.higherplants,pathwayin
Figure 4-5
INTERMEMBRANESPACEExternal (rotenone-insensitive)Theubiguinone(UQ)pooldiffusesCytochromecisaperipheralNAD(P)Hdehydrogenasescanacceptfreelywithintheinnermembraneandproteinthattransfers electronselectronsdirectlyfromNAD(P)HservestotransferelectronsfromthefromcomplexillltocomplexiV.Innerproduced inthecytosol.dehydrogenasestoeithercomplex lllmembraneorthealternativeoxidase.NADP+NAD+NADHNADPH4H4H2H3HCazCa24CytcUQAOXF,7H20Succinate023HNADPHNADHNADHFumarateH.OComplexIllComplexINNADPNAD+NADCytochromebcCytochromeComplexllcomplexoxidaseSuccinateRotenone-insensitiveComplex!ATPdehydrogenaseNAD(P)HdehydrogenasesNADHADP+?existonthematrixsidedehydrogenaseAnalternativeoxidase (AOx)ofthemembrane.ComplexVaccepts electrons directlyATPsynthasefromubiquinoneMATRIXFigure 4-6FIGURE11.8Organizationoftheelectrontransportchainenzymespumpsprotons.Specificinhibitors,rotenoneforand ATPsynthesisintheinnermembraneofplantmito-complexI,antimycinforcomplexIl,cyanideforcomplexchondria,Inaddition to the five standard protein com-IV,andsalicylhydroxamicacid(SHAM)forthealternativeplexesfound in nearlyall othermitochondria,the electronoxidase,areimportanttoolstoinvestigatetheelectrontransportchain ofplantmitochondriacontains fiveaddi-transportchain.ofplantmitochondria.tional enzymes marked ingreen.None of these additional
Figure 4-6
NADP+NAD+NADPHNADHIntermembranespaceComplexIllInnerUQorComplexImembranepoolAlternativeoxidaseMatrixNAD+NADPNADHNADPHFigure 14.25Rotenone-insensitive NADH and NADPH dehydrogenases of the inner mitochon-drial membrane.In addition to ComplexI,plant mitochondria possess simpler(single polypeptide)dehydrogenases onboth surfaces of the mitochondrial innermembrane.These do not pump protons and are insensitive to ComplexI inhibitors such as rotenone. Four dehydrogenases have been described, although notall of thesemay occur in all plant tissues.The two external dehydrogenases arethought to oxidize cytosolic NAD(P)H and feed electrons into the UQ pool. Thetwo enzymes on the inner surface provide additional routesfor oxidation of theNADH and NADPH formed in the matrix.The proteins involved in these pro-cesseshavenot yetbeenfirmlyidentified.Figure 4-6-0
Figure 4-6-0
Intermembrane20tnspace[N-2]eFe/SUOFigure 4-6-1UQUQH2Figure14.19Proposed structureand membranetopographyof miUQH22Htochondrial complexI (NADH:UQoxidoreductase)MatrixHThecomplexacts asan NADH-ubiquinone oxidoreductasetransferringelectrons frommatrixNADH2H+to ubiquinone.This transfer involves FMN,fourNADHiron-sulfur centers (N1-N4)andan internal quinone(UQ).TheH/2eratioisthoughttobefour,withtwo Htaken up at the internal quinone site and an[N-1,N-3,N-4]othertwotranslocated bya poorlydefined mechaNADFe/Snism (dotted line).Thecomplex isreadilybrokenintotwosmallercomplexes,oneofwhich(blue)isFMNvery hydrophobic and contains all of the subunitsencoded inthemitochondrion.Theotherarmof theComplexIcomplex(purple)protrudes intothematrixandis(600kDa)composed of nucleus-encoded subunits
Figure 4-6-1
Figure 4-6-2UOFigure14.21Proposed structure andmembrane topographyof89mitochondrial ComplexII(succinate:ubiquinoneUQHcytboxidoreductasewolargehydrophilicperipheralsubunits that make up succinate dehydrogenase areS-3bound to the innermembrane through two smallhydrophobicmembrane-spanning subunits.CovaS-1/S-220lentlyboundflavinadeninedinucleotide(FAD)isFADassociated withthesubunitFflavinprotein"yellow)whfr(2?S-3)areboundtol(ironprotein"brown).Thetwohydrophobicsubunits containoneb-typecytochromeandaubiquinone（UQ)pairtheexactlocationsofwhichareuncertain.TheproposedpathofSuccinateelectronflowissuccinate-FAD-S-1/S-2-S-3-theComplex IIUQpair-aUQmoleculefromthemitochondrial(125 kDa)FumarateUQ pool
Figure 4-6-2
(A)(B)IntermembranespaceCyteCytereCytci20+?UQHTUQFe-SFe-SCenterPebs66DEeebs60been?UQ+HFigure14.22CenterN(A)Diagram illustratingproposed structure1UQH2andmembranetopographyofmitochondrialComplex IIl (ubiquinone:cytochrome-coxidoreductase,alsoknownascytochromebc,).Thecomplexisadimer,witheachmonomercon-tainingmultiplesubunits.Ubiquinol (UQH)is oxidized at Center Pwhile ubiquinone(UQ)isreduced at CenterN.Thetwo electrons fromUQH, take divergent paths, one being trans-ferred tomobile cytochrome cviaa Rieskeiron-sulfurcenterand cytochrome C,the otherreachingCenterNviatwob-type cytochromesThe inhibitory sites ofantimycin and myxothiazol are at Centers Nand P, respectivelyComplexIllFigure 4-6-3(B)Crystal structureofa dimericmammalian(500kDa)Matrixcytochromebc,complex
Figure 4-6-3