Methane formation from acetyl phosphate in cell extracts of Methanosarcina barkeri Dependence of the reaction on coenzyme A

Cell extracts (100 000 × g supernatant) of acetate grown Methanosarcina barkeri (strain MS) catalyzed the formation of methane from acetyl phosphate (apparent K m ∼ 2 mM) with specific activities up to 50 nmol·min −1 ·mg protein −1 , which is 25% of the specific rate of methane formation from acetate by intact cells. Methane formation from acetyl phosphate was strictly dependent on coenzyme A (CoA) (apparent K m ∼ 0.1 mM), which was demonstrated with extracts pretreated with charcoal to remove endogenous CoA. The extracts contained high specific activities of acetate kinase (16 μmol·min −1 ·mg protein −1 ) and of phosphotransacetylase (26 μmol·min −1 ·mg protein −1 ). The findings indicate that methanogenesis from acetate proceeds via acetyl phosphate and acetyl‐CoA as intermediates. Almost identical results were obtained with cell extracts of acetate grown M. barkeri (strain Fusaro).