INTERMEMBRANE SPACE Extemal (rotenone-insensitive) The ubiquinone(UQ) pool diffuses NAD(P)H dehydrogenases can accept freely within the innermembrane and Cytochrome c is a peripheral electrons directly from NAD(P)H protein that transfers electron serves to transfer electrons from the n from complex ill to complex IV ner produced in the cytosol membrane dehydrogenases to either complex lll or the alternative oxidase NAD NADP NADH NADPH 2 3 yt c AOX Succinate HO NADH NADH NADPH Fumarate H2o Complex l Complex IV NADT NAD+ NADP. Complex ll Cytochrome bG, Cytochrome Succinate complex Complex I Rotenone-insensitive dehydrogenase ATP ( ADP)+(P) of the membra An alternative oxidase ( AOX) accepts electrons directly Complex V from ubiquinone ATP synthase MATR Figure 4-6 FIGURE 11.8 Organization of the electron transport chain enzymes pumps protons. Specific inhibitors, rotenone for and ATPsynthesis in the inner membrane of plant mito- complex I, antimycin for complex Ill, cyanide for complex chondria. In addition to the five standard protein com- IV, and salicylhydroxamic acid(SHAM)for the alternative plexes found in nearly all other mitochondria, the electron oxidase, are important tools to investigate the electron transport chain of plant mitochondria contains five addi transport chain of plant mitochondria. tional enzymes marked in green. None of these additional
Figure 4-6
:NADH NAD+=NADPH(NADP Intermembrane space Inner Complex Ill membrane Complex I or pool Alternati xida Matrix NADH (NADT NADPH(NADP Figure 14.25 drial membrane. In addition to Complex I, plant mitochondria possess simpler on Rotenone-insensitive NADH and NADPH dehydrogenases of the inner mitochon membrane.These do not pump protons and are insensitive to Complex I inhi.> (single polypeptide) dehydrogenases on both surfaces of the mitochondrial inn bitors such as rotenone. Four dehydrogenases have been described, although not all of these may occur in all plant tissues. The two external dehydrogenases are thought to oxidize cytosolic NAD(P)H and feed electrons into the UQ pool. The two enzymes on the inner surface provide additional routes for oxidation of the NADH and NADPH formed in the matrix. The proteins involved in these pro- cesses have not yet been firmly identified Figure 4-6-0
Figure 4-6-0