Spectroscopic and enzymatic evidence for membrane-bound electron transport carriers and hydrogenase and their relation to cytochromebfunction inMethanosarcina barkeri

Membranes prepared from Methanosarcina barkeri cultured on acetate were examined for electron carriers using electron paramagnetic resonance (EPR) and optical spectroscopy. EPR analysis of membrane suspensions demonstrated multiple iron-sulfur centers of the 4Fe-4S type, a hihg-spin heme-like species and possibly rebredoxin. Optical spectroscopy demonstrated that a b-type cytochrome was reduced by molecular hydrogen and oxidized by methyl coenzyme M. A membrane-bound hydrogenase activity (14 μM · min−1 (mg protein)−1) was detected. This suggests a putative role for cytochrome b and hydrogenase in electron transfer and methyl-group reduction during aceticlastic methanogenesis.