Figure 1.

General approach of methionine metabolism (modified from [46]). L-Methionine is mainly supplied exogenously from dietary proteins. The enzymes involved in this pathway are (1) methionine adenosyltransferase; (2) S-adenosylmethionine methyltransferases; (3) adenosylhomocysteinase; (4) 5-methyltetrahydrofolate-homocysteine methyltransferase (in mammals betaine-homocysteine methyltransferase or homocysteine methyltransferase); (5) cystathionine-γ-synthase; (6) cystathionine-γ-lyase; (7) α-ketoacid dehydrogenase.