This enzyme is crucial for maintaining the one carbon metabolism, specifically the folate cycle.

Physiologically speaking, one crucial enzyme in the folate cycle is methionine synthase, which incorporates the coenzyme cobalamin (also known as Vitamin B12).

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.

[2] 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:NADP+ oxidoreductase.