Fig. 1

Metabolism of homocysteine. Transsulfuration proceeds by first condensing homocysteine with serine, producing cystathionine. Hydrolysis of cystathionine by cystathionase yields cysteine and α-ketobutyrate. Remethylation of homocysteine by betaine-homocysteine methyl transferase-catalyzed transfer of an N-methyl group from betaine to homocysteine, yielding methionine and N, N-dimethylglycine.