Effect of methanogenic substrates on coenzyme F-dependent N,N-methylene-HMPT dehydrogenase, N,N-methenyl-HMPT cyclohydrolase and F-reducing hydrogenase activities in Methanosarcina barkeri.

We measured F-dependent N,N-methylenetetrahydro-methanopterin dehydrogenase, N, N-methenyltetrahydro-methanopterin cyclohydrolase, and F-reducing hydrogenase levels in Methanosarcina barkeri grown on various substrates. Variation in dehydrogenase levels during growth on a specific substrate was usually <3-fold, and much less for cyclohydrolase. H−CO-, methanol-, and H−CO+ methanol-grown cells had roughly equivalent levels of dehydrogenase and cyclohydrolase. In acetate-grown cells cyclohydrolase level was lowered 2 to 3-fold and dehydrogenase 10 to 80-fold; this was not due to repression by acetate, since, if cultures growing on acetate were supplemented with methanol or H−CO, dehydrogenase levels increased 14 to 19-fold, and cyclohydrolase levels by 3 to 4-fold. Compared to H−CO- or methanol-grown cells, acetate-or H−CO + methanol-grown cells had lower levels of and less growth phase-dependent variation in hydrogenase activity. Our data are consistent with the following hypotheses: 1. M. barkeri oxidizes methanol via a portion of the CO-reduction pathway operated in the reverse direction. 2. When steps from CO to CH-S-CoM in the CO-reduction pathway (in either direction) are not used for methanogenesis, hydrogenase activity is lowered. [ABSTRACT FROM AUTHOR]