On the role of N‐7‐mercaptoheptanoyl‐O‐phospho‐L‐threonine (component B) in the enzymatic reduction of methyl‐coenzyme M to methane

Abstract The reduction of methyl-coenzyme M (CH 3 SCoM) to methane in methanogenic bacteria is dependent on component B ( N -7-mercaptoheptanoyl- O -phospho-L-threonine, HSHTP). We report here that S -methyl-component B ( N -7-(methylthio)heptanoyl- O -phospho-L-threonine, CH 3 SHTP) can substitute for neither CH 3 SCoM nor HSHTP in the methyl-CoM reductase reaction. Rather, CH 3 SHTP proved to be an inhibitor competitive with HSHTP (apparent K i =6 μM) and noncompetitive with CH 3 SCoM. These results make it very unlikely that HSHTP functions as a methyl group carrier. A role for HSHTP as direct electron donor for CH 3 SCoM reduction to CH 4 is proposed.