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Review
. 2008 Feb;190(3):784-91.
doi: 10.1128/JB.01422-07. Epub 2007 Nov 26.

Energy conservation via electron-transferring flavoprotein in anaerobic bacteria

Gloria Herrmann  1 , Elamparithi Jayamani, Galina Mai, Wolfgang Buckel
Affiliations
Review

Energy conservation via electron-transferring flavoprotein in anaerobic bacteria

Gloria Herrmann et al. J Bacteriol. 2008 Feb.
No abstract available

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Figures

FIG. 1.
FIG. 1.
Traditional scheme of glutamate fermentation via 3-methylaspartate in C. tetanomorphum. Five pyruvates derived from 5 glutamates are oxidized by 5 ferredoxins to 5 CO2 and 5 acetyl-CoA. The 5 reduced ferredoxins (Fd2−) formed are reoxized by 2 H+ and 4 NAD+, yielding 1 H2 and 4 NADH, respectively. Four of the 5 acetyl-CoA formed are reduced by 4 NADH to 2 butyryl-CoA (see Fig. 2). Three ATP are generated from 2 butyryl-CoA and the remaining 1 acetyl-CoA (see Fig. 5).
FIG. 2.
FIG. 2.
Butyrate synthesis from 2 acetyl-CoA in members of the genus Clostridium.
FIG. 3.
FIG. 3.
Different functions of Etf. (A) In aerobic organisms Etf transfers the electrons from butyryl-CoA dehydrogenase in the cytoplasm or mitochondrial matrix to ubiquinone (UQ), which is mediated by the integral membrane enzyme Etf-quinone oxidoreductase. (B) In anaerobic bacteria Etf transfers the electrons from NADH to the cytosolic butyryl-CoA dehydrogenase, which reduces crotonyl-CoA. (C) Additional reduction of ferredoxin by the Etf-butyryl-CoA dehydrogenase complex as proposed in this work.
FIG. 4.
FIG. 4.
Hydroxyglutarate pathway of glutamate fermentation proposed here. Note that 3 of 5 crotonyl-CoA are oxidized to 6 acetyl-CoA by 3 NAD+. Two of the 3 NADH formed and the 1 NADH recycled are used to reduce 2 crotonyl-CoA to 2 butyryl-CoA, which drives the reduction of 2 ferredoxins by the other 2 NADH. One ferredoxin reduces protons to H2, and the other reduces NAD to NADH, which is recycled. Hase = hydrogenase (Hyd); ETF-BuDH, Etf-Bcd complex; Fd2−, reduced ferredoxin.
FIG. 5.
FIG. 5.
Methylasparate pathway of glutamate fermentation proposed here (see Fig. 1). Note that 4 acetyl-CoA are reduced by 4 NADH to 2 butyryl-CoA; the fifth NADH and the 1 recycled NADH are used to reduce 2 ferredoxins, driven by the reduction of crotonyl-CoA to butyryl-CoA. BS, butyrate-synthesizing enzymes, including the Etf-Bcd complex; Fd2−, reduced ferredoxin.
FIG. 6.
FIG. 6.
Proposed catabolism of C. kluyveri. Substrates and products are indicated by bold type.
See this image and copyright information in PMC

References

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    1. Barker, H. A. 1961. Fermentations of nitrogenous organic compounds, p. 151-207. In I. C. Gunsalus and R. Y. Stanier (ed.), The bacteria, vol. 2. Academic Press Inc., New York, NY.
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    1. Beckmann, J. D., and F. E. Frerman. 1985. Electron-transfer flavoprotein-ubiquinone oxidoreductase from pig liver: purification and molecular, redox, and catalytic properties. Biochemistry 243913-3921. - PubMed
    1. Boiangiu, C. D., E. Jayamani, D. Brügel, G. Herrmann, J. Kim, L. Forzi, R. Hedderich, I. Vgenopoulou, A. J. Pierik, J. Steuber, and W. Buckel. 2005. Sodium ion pumps and hydrogen production in glutamate fermenting anaerobic bacteria. J. Mol. Microbiol. Biotechnol. 10105-119. - PubMed

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