The reduction of methyl-CoM to methane in methanogenic bacteria is dependent on a low-M r, heat-stable compound designated component B, the structure of which has recently been assigned as N-7-mercaptoheptanoyl-O-phosphothreonine. We report here that only the enantiomer derived from O-phospho-L-threonine has cofactor activity. N-7-Mercaptoheptanoyl-O-phospho-D-threonine was neither active nor inhibitory.
