Structure of purified cytoplasmic cofactor from Methanobacterium thermoautotrophicum

The reduction of methylcoenzyme M to methane is known to require a heat stable and oxygen sensitive cofactor. Recently it has been shown that the active site of this cofactor is 7-mercaptoheptanoylthreonine phosphate. The present study shows that in the complete structure of this cofactor 7-mercaptoheptanoylthreonine phosphate is linked by pyrophosphate to two N-acetyl-glucosamine residues and an unidentified terminal group R with m/z 214. By fast-atom-bombardment mass spectrometry the intact cofactor, isolated as the mixed disulfide with 2-mercaptoethanol, was shown to have a molecular weight of 1084.5. The pyrophosphate bond is quite labile and undergoes hydrolysis or prolonged storage. This lability of the pyrophosphate bond may explain why the intact cofactor has not been isolated until now.