Component C of the methylreductase system of Methanobacterium.

Component C of the methyl coenzyme M methylreductase system of Methanobacterium thermoautotrophicum has been purified to homogeneity with a 17% recovery of initial units. The native protein has a molecular weight of 300,000 and is composed of three different subunits with masses of 68,000, 45,000, and 38,500. They are present in equal proportion, suggesting a stoichiometry of alpha 2, beta 2, gamma 2 in the native protein. The amino acid composition reveals a preponderance of acidic amino acid residues. The protein is yellow, having an absorption maximum at 425 nm and a shoulder at 455 nm. Reconstitution of the methyl coenzyme M methylreductase activity was linearly dependent on added component C. Component C has been detected in cell extracts of other methanogens.