Acetyl-CoA pathway of autotrophic growth. Identification of the methyl-binding site of the CO dehydrogenase.
CO dehydrogenase, a key enzyme of the acetyl-CoA pathway of autotrophic growth, has been methylated using 14CH3I or 14CH3-corrinoid enzyme plus ferredoxin. Acetyl-CoA was synthesized from the resulting 14CH3-CO dehydrogenase, CO, and CoASH, with about 50% yield of the available 14C and without addition of other enzymes except CO dehydrogenase disulfide reductase. Even the reductase could be replaced by dithioerythritol. Amino acid analysis of the 14CH3-CO dehydrogenase showed two radioactive peaks, one of which migrated as S-methylcysteine but very close to the methyl ester of glutamic acid. By oxidation with H2O2, the radioactive component of this peak was identified as S-methylcysteine sulfone. Amino acid analysis of the 14CH3-CO dehydrogenase after synthesis of acetyl-CoA demonstrated that there was a large decrease in radioactivity of the peak containing the S-methyl-cysteine. The compound present in the second peak has not been identified; there was no decrease in its radioactivity. By nonreducing gel electrophoresis of the 14CH3-CO dehydrogenase, followed by autoradiography, it was shown that the beta subunit is the methyl acceptor. These results demonstrate that a cysteine of the beta subunit is the methyl acceptor and that CO dehydrogenase per se catalyzes the synthesis of acetyl-CoA.
Pezacka
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Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio 44106.
Wood
H G
HG
D000105:Acetyl Coenzyme A / Q000378:metabolism*; D000445:Aldehyde Oxidoreductases / Q000378:metabolism*; D001665:Binding Sites; D003013:Clostridium / Q000254:growth & development* / Q000378:metabolism; D007700:Kinetics; D008745:Methylation; D008962:Models, Theoretical; D009097:Multienzyme Complexes
D009097:Multienzyme Complexes; D000105:Acetyl Coenzyme A; D000445:Aldehyde Oxidoreductases; C019823:carbon monoxide dehydrogenase