Methyltrophic corrinoid proteins must have the cobalt atom in the active cobalt(I) state to become methylated. Because the cobalt(I)/cobalt(II) transformation has a very low redox potential the corrinoid cofactor is subject to adventitious oxidation to the cobalt(II) state, which renders the proteins inactive. This enzyme, characterized from the methanogenic archaeon Methanosarcina barkeri, reduces cobalt(II) back to cobalt(I), restoring activity. The enzyme acts on the corrinoid proteins involved in methanogenesis from methylamine, dimethylamine, and trimethylamine, namely MtmC, MtbC, and MttC, respectively. While in vitro the enzyme can use Ti(III)-citrate as the electron donor, the in vivo donor is not known. The enzyme from Methanosarcina barkeri contains a C-terminal [4Fe-4S] ferredoxin-like domain.