Analysis of hydrogen metabolism in Methanosarcina barkeri: Regulation of hydrogenase and role of CO-dehydrogenase in H2 production

Abstract

Methanosarcina barkeri strain MS had significant levels of in vivo hydrogenase activity and both produced and consumed hydrogen when grown on CO or methanol as sole carbon and energy source. The activities of multiple hydrogenases were detected in extracts and cells of M. barkeri grown on CO or methanol. Uptake hydrogenase activity was 4 times higher and production hydrogenase was 3 times lower in methanol than in CO-grown cells. When 2-bromoethane sulfonate was added to M. barkeri growing on methanol, methane production was inhibited while hydrogen was produced but not consumed, indicating that hydrogen may be an intermediate in methane production from methanol. CO inhibited in vivo hydrogenase activity of M. barkeri cells suggesting that CO might inhibit uptake hydrogenase activity and not production hydrogenase activity. Purified CO-dehydrogenase (CODH) from M. barkeri produced 278.9 nmol hydrogen min−1· mg−1 protein using methyl viologen as electron carrier. Purified CODH did not display either detectable uptake hydrogenase activity or significant tritium exchange activity. Notably, 20 μM KCN inhibited both hydrogen producing and CO-oxidizing activity of purified CODH, but not uptake hydrogenase activity. Thus, we propose that in addition to its role in acetate synthesis and degradation, CODH produces hydrogen as a by-product of carbonyl group transformation.