title: Acetate biosynthesis by acetogenic bacteria. Evidence that carbon monoxide dehydrogenase is the condensing enzyme that catalyzes the final steps of the synthesis.
abstract: The purified carbon monoxide dehydrogenase from Clostridium thermoaceticum is the only protein required to catalyze an exchange reaction between carbon monoxide and the carbonyl group of acetyl-CoA. This exchange requires that the CO dehydrogenase bind the methyl, the carbonyl, and the CoA groups of acetyl-CoA, then equilibrate the carbonyl with CO in the solution and re-form acetyl-CoA. CoA is not necessary for the exchange and, in fact, inhibits the reaction. These studies support the view that CO dehydrogenase is the condensing enzyme that forms acetyl-CoA from its component parts. Carbon dioxide also exchanges with the C-1 of acetyl-CoA, but at a much lower rate than does CO. At 50 degrees C and pH 5.3, the optimal pH, the turnover number is 70 mol of CO exchanged per min/mol of enzyme. Low potential electron carriers are stimulatory. The Km app for stimulation by ferredoxin is 50-fold less than the value for flavodoxin. Neither ATP or Pi stimulate the exchange. The EPR spectrum of the CO-reacted enzyme is markedly changed by binding of CoA or acetyl-CoA. Arginine residues of the CO dehydrogenase appear to be involved in the active site, possibly by binding acetyl-CoA. Mersalyl acid, methyl iodide, 5,5-dithiobis-(2-nitrobenzoate), and sodium dithionite inhibit the exchange reaction. A scheme is presented to account for the role of CO dehydrogenase in the exchange reaction and in the synthesis of acetate.
authors.forename: S W
authors.initials: SW
authors.lastname: Ragsdale
authors.forename: H G
authors.initials: HG
authors.lastname: Wood
mesh_terms: D000085:Acetates / Q000096:biosynthesis*; D019342:Acetic Acid; D000105:Acetyl Coenzyme A / Q000378:metabolism; D000445:Aldehyde Oxidoreductases / Q000302:isolation & purification / Q000378:metabolism*; D003013:Clostridium / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D004591:Electrophoresis, Polyacrylamide Gel; D008956:Models, Chemical; D008970:Molecular Weight; D009097:Multienzyme Complexes
chemical_list: D000085:Acetates; D009097:Multienzyme Complexes; D000105:Acetyl Coenzyme A; D000445:Aldehyde Oxidoreductases; C019823:carbon monoxide dehydrogenase; D019342:Acetic Acid