Role of vitamin B ₁₂ in methyl transfer for methane biosynthesis by Methanosarcina barkeri

When Methanosarcina barkeri is grown on methanol as the sole carbon source, a B ₁₂ -containing protein is synthesized by this organism. This B ₁₂ protein contains bound aquocobalamin, and when this cofactor is reduced and methylated with [ ¹⁴ C]methyl iodide, the resultant [ ¹⁴ C]methyl B ₁₂ protein is extremely active in the biosynthesis of ¹⁴ C-labeled methane. These findings indicate that a B ₁₂ -dependent system is operative in the biological formation of methane in addition to other systems that are B ₁₂ -independent.