The process whereby an amino acid donates its terminal methyl (-CH3) group for methylation of other compounds. Methionine is the principal methyl donor in the body and the donated methyl group may subsequently be involved in the synthesis of such compounds as choline or creatinine or in detoxification processes.
The process in the metabolism of amino acids in which a methyl group is transferred from one compound to another; for example, the conversion in the body of homocysteine to methionine. In this case, the methyl group is furnished by choline or betaine.