 Regeneration requires reductive methylation via a reaction catalyzed by (methionine synthase) reductase in which S-adenosylmethionine is utilized as a methyl donor, reducing cob(II)alamin to cob(I)alamin.This enzyme belongs to the family of oxidoreductases, to be specific those oxidizing metal ion with NAD+ or NADP+ as acceptor.The systematic name of this enzyme class is [methionine synthase]-methylcob(I)alamin,S-adenosylhomocysteine