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