Catabolic enzymes of the acetogen Butyribacterium methylotrophicum grown on single-carbon substrates.

When grown on formate, formate-CO, and methanol-CO, Butyribacterium methylotrophicum contained high levels of tetrahydrofolate (H4folate) and required enzymes, carbon monoxide dehydrogenase, formate dehydrogenase, and hydrogenase. The activities of methylene-H4folate reductase were comparable to other H4 folate activities (which ranged from 0.55 to 9.28 mumol/min per mg of protein) when measured by an improved procedure. The H4folate activities in formate-grown cells were twice those found in formate-CO-grown cells. This result correlated with a growth yield on formate that was one-half that on formate-CO. The stoichiometry of the formyl-H4folate synthetase reaction was 1 mol of ATP per 1 mol of formate. The methylene-H4folate dehydrogenase was NAD+ dependent. We conclude that B. methylotrophicum utilizes these enzymes in homoacetogenic catabolism.