Activities of formylmethanofuran dehydrogenase, methylenetetrahydromethanopterin dehydrogenase, methylenetetrahydromethanopterin reductase, and heterodisulfide reductase in methanogenic bacteria.

The activities of formylmethanofuran dehydrogenase, methylenetetrahydromethanopterin dehydrogenase, methylenetetrahydromethanopterin reductase, and heterodisulfide reductase were tested in cell extracts of 10 different methanogenic bacteria grown on H/CO or on other methanogenic substrates. The four activities were found in all the organisms investigated: Methanobacterium thermoautotrophicum,M. wolfei, Methanobrevibacter arboriphilus, Methanosphaera stadtmanae, Methanosarcina barkeri (strains Fusaro and MS), Methanothrix soehngenii, Methanospirillum hungatei, Methanogenium organophilum, and Methanococcus voltae. Cell extracts of H/CO grown M. barkeri and of methanol grown M. barkeri showed the same specific activities suggesting that the four enzymes are of equal importance in CO reduction to methane and in methanol disproportionation to CO and CH. In contrast, cell extracts of acetate grown M. barkeri exhibited much lower activities of formylmethanofuran dehydrogenase and methylenetetrahydromethanopterin dehydrogenase suggesting that these two enzymes are not involved in methanogenesis from acetate. In M. stadtmanae, which grows on H and methanol, only heterodisulfide reductase was detected in activities sufficient to account for the in vivo methane formation rate. This finding is consistent with the view that the three other oxidoreductases are not required for methanol reduction to methane with H. [ABSTRACT FROM AUTHOR]