activated methyl cycle

activated methyl cycle A series of reactions in which S-methyl groups from methionine are converted into a biochemically reactive form through insertion into an adenosyl group; an active S-methyl group can be transferred from S-adenosylmethionine to acceptor molecules such as norepinephrine. The remaining part of the cycle includes the regeneration of methionine from homocysteine and N5- methyltetrahydrofolate.