Methyl coenzyme M reductase from Methanobacterium thermoautotrophicum. Resolution and properties of the components

Abstract

Oxygen-labile extract of Methanobacterium thermoautotrophicum was resolved into three components, A, B, and C, that were required for the reductive demethylation of methyl coenzyme M, 2-(methylthio)-ethanesulfonate, in the presence of molecular hydrogen. Components A and C were found to be large heat-labile proteins with A being in excess of 500,000 daltons, and C being 130,000 daltons. Component A exhibited hydrogenase activity for reduction of viologen dyes, coenzyme F420, or flavins but not for NAD+ or NADP+. An apparent Km of 25 microM was determined for F420 and a Km of 1.5 mM for methyl viologen. After centrifugation at 100,000 x g for 1 h, 80% of Component A was found in the supernatant solution. Component B was found to be an oxygen-labile, heat-resistant, dialyzable cofactor with a size of about 1,000 daltons and with no apparent absorption in the visible range. Known cofactors failed to substitute for the new coenzyme.