Acetate formation from CO and CO2 by cell extracts of Peptostreptococcus productus (strain Marburg)

Abstract

Cell extracts of Peptostreptococcus productus (strain Marburg) obtained from CO grown cells mediated the synthesis of acetate from CO plus CO2 at rates of 50 nmol/min × mg of cell protein. 14CO was specifically incorporated into C1 of acetate. No label exchange occurred between 14C1 of acetyl-CoA and CO, indicating that 14CO incorporation into acetate was by net synthesis rather than by an exchange reaction. In acetate synthesis from CO plus CO2 the latter substrate could be replaced to some extent by formate or methyl tetrahydrofolate as the methyl donor. The methyl group of methyl cobalamin was incorporated into acetate ony at very low activities. The cell extracts contained high levels of enzyme activities involved in acetate or cell carbon synthesis from CO2. The following enzymic activities were detected: CO: methyl viologen oxidoreductase, formate dehydrogenase, formyl tetrahydrofolate synthetase, methenyl tetrahydrofolate cyclohydrolase, methylene tetrahydrofolate dehydrogenase, methylene tetrahydrofolate reductase, phosphate acetyltransferase, acetate kinase, hydrogenase, NADPH: benzyl viologen oxidoreductase, and pyruvate synthase. Some kinetic and other properties were studied.