Betaine homocysteine methyltransferase (BHMT), a cytosolic enzyme, and its partial fragments were discovered as autolysosomal membrane proteins from rat liver in the presence of leupeptin. BHMT was also found in human liver. BHMT transfers a methyl group from betaine to homocysteine to form DMG (dimethylglycine) and Met. In vivo, liver BHMT expression is influenced by dietary changes in sulphur amino acids, choline and betaine.