Catalyzes the transfer of the methyl group from monomethylamine to the corrinoid cofactor of MtmC (MtmC1 or MtmC2). Co(I)-[methylamine-specific corrinoid protein] + H(+) + methylamine = methyl-Co(III)-[methylamine-specific corrinoid protein] + NH4(+) One-carbon metabolism; methanogenesis from methylamine. Dimer of homotrimers. Can form a complex with MtmC (MtmC1 or MtmC2). MtmB1 transcript is abundant relative to the mtmB2 transcript. Belongs to the monomethylamine methyltransferase family. Life's jokers - Issue 25 of August 2002