A novel mode of lactate metabolism in strictly anaerobic bacteria.
Lactate is a common substrate for major groups of strictly anaerobic bacteria, but the biochemistry and bioenergetics of lactate oxidation is obscure. The high redox potential of the pyruvate/lactate pair of E0 ' = -190 mV excludes direct NAD(+) reduction (E0 ' = -320 mV). To identify the hitherto unknown electron acceptor, we have purified the lactate dehydrogenase (LDH) from the strictly anaerobic, acetogenic bacterium Acetobacterium woodii. The LDH forms a stable complex with an electron-transferring flavoprotein (Etf) that exhibited NAD(+) reduction only when reduced ferredoxin (Fd(2-) ) was present. Biochemical analyses revealed that the LDH/Etf complex of A. woodii uses flavin-based electron confurcation to drive endergonic lactate oxidation with NAD(+) as oxidant at the expense of simultaneous exergonic electron flow from reduced ferredoxin (E0 ' ≈ -500 mV) to NAD(+) according to: lactate + Fd(2-)  + 2 NAD(+)  → pyruvate + Fd + 2 NADH. The reduced Fd(2-) is regenerated from NADH by a sequence of events that involves conversion of chemical (ATP) to electrochemical ( Δ μ ˜ Na + ) and finally redox energy (Fd(2-) from NADH) via reversed electron transport catalysed by the Rnf complex. Inspection of genomes revealed that this metabolic scenario for lactate oxidation may also apply to many other anaerobes.
Molecular Microbiology and Bioenergetics, Institute of Molecular Biosciences, Goethe University Frankfurt, Frankfurt am Main, Germany.
Marie Charlotte
MC
Weghoff
Johannes
J
Bertsch
Volker
V
Müller
D045855:Acetobacterium / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism*; D001421:Bacteria, Anaerobic / Q000378:metabolism*; D002384:Catalysis; D004579:Electron Transport; D044927:Electron-Transferring Flavoproteins / Q000378:metabolism*; D004583:Electrons; D004734:Energy Metabolism; D005288:Ferredoxins / Q000378:metabolism; D007770:L-Lactate Dehydrogenase / Q000378:metabolism*; D019344:Lactic Acid / Q000378:metabolism*; D009243:NAD / Q000378:metabolism; D010084:Oxidation-Reduction; D012964:Sodium / Q000378:metabolism
D044927:Electron-Transferring Flavoproteins; D005288:Ferredoxins; D009243:NAD; D019344:Lactic Acid; D012964:Sodium; D007770:L-Lactate Dehydrogenase