Pyruvate-flavoprotein oxidoreductase

Not only are two molecules of ATP hydrolyzed to pump each electron, but the Fe-protein must receive electrons from a powerful (low E°) reductant such as reduced ferredoxin, reduced flavodoxin, or dithionite. Klebsiella pneumoniae contains a pyruvate flavodoxin oxidoreductase (Eq. 15-35) that reduces either flavodoxin or ferredoxin to provide the low potential electron donor.29 30 In some bacteria, e.g., the strictly aerobic Azotobacter, NADPH is the electron donor for reduction of N2. The Fe-protein is thought to accept electrons from a chain that includes at least the ordinary bacterial ferredoxin (Fd) and a special one-electron-accepting azotoflavin, a flavoprotein that is somewhat larger than the flavodoxins (Chapter 15) and appears to play a specific role in N2 fixation.31 In Clostridium and Rhizobium reduced ferredoxins generated by cleavage of pyruvate reduce nitrogenase directly.32... 

FIGURE 9.2 Physiology of ABE fermentation metabolism of Clostridium acetobutylicum with the respective enzymes and products. CoA, coenzyme A Ldh, lactate dehydrogenase Pdc, pyruvate decarboxylase Pfor, pyruvate ferredoxin oxidoreductase Fdred, ferredoxin reduced Thl, thiolase Hbd, p-hydroxybutyryl-CoA dehydrogenase Crt, crotonase Bed, butyryl-CoA dehydrogenase Etf, electron transfer flavoprotein Pta, phosphotransacetylase Ack, acetate kinase Ptb, phosphotransbutyrylase Buk, butyrate kinase Ctf A/B, acetoacetyl-CoA acyl-CoA transferase Adc, acetoacetate decarboxylase AdhE, aldehyde/alcohol dehydrogenase Bdh, butanol dehydrogenase. 

Fig. 5.2. Possible metabolic pathways in facultative anaerobic mitochondria. Shaded boxes show components of the electron-transport chain used during hypoxia, open boxes are components used during aerobiosis, and the hatched boxes (complex I and ATP-synthase) are components used under aerobic as well as anaerobic conditions. ASCT acetate succinate CoA-transferase, C cytochrome c, Cl, CIII and CIV complexes I, III and IV of the respiratory chain, CITR citrate, ECR enoyl-CoA reductase (such as present in Ascaris suum), ETF electron-transfer flavoprotein, ETF RQ OR electron-transfer flavoproteimrhodoquinone oxidoreductase, FRD fumarate reductase, FUM fumarate, MAE malate, OXAC oxaloacetate, PYR pyruvate, RQ rhodoquinone, SDH succinate dehydrogenase, SUCC succinate, Succ-CoA succinyl-CoA, TER trans-2-enoyl-CoA reductase (such as present in E. gracilis), UQ ubiquinone...

Fig. 13.1.1. Schematic overview of mitochondrial oxidative phosphorylation. A part of the mitochondrion is represented, showing the outer mitochondrial membrane (OMM), inner mitochondrial membrane (IMM) and crista (an invagination of the inner membrane). Substrates for oxidation enter the mitochondrion through specific carrier proteins, e.g., the pyruvate transporter, (PyrT). Reducing equivalents from fatty acyl CoA dehydrogenases, pyruvate dehydrogenase and the TCA cycle are delivered to the electron transport chain through NADH, succinate ubiquinol oxidoreductase (SQO), electron transfer flavoprotein (ETF) and its ubiquinol-...

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