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Methionine

L-methionine is a sulfur-containing amino acid that removes heavy metals, quenches free radicals, and lowers cholesterol. L-Methionine also prevents fat accumulation in the liver and, along with cysteine/cystine, helps prevent disorders of the hair, skin, and nails. Methionine is metabolised in man via a multi-step pathway, the transsulfuration pathway. Several intermediate products are formed in this pathway, which play a dominant role in other biochemical pathways as well. Regarding human nutrition, l-methionine is an essential amino acid whereas d-methionine is non-nutritive. For purposes of metabolism, l-methionine via S-adenosylmethionine has an important methylating function. In its activated form, S-adenosylmethionine, methionine is the methyl donor in hundreds of biological transmethylation reactions. Moreover, methionine is the propylamine donor in polyamine synthesis. The ultimate product resulting from the demethylation of methionine is homocysteine, the remethylation of which is catalyzed by a cobalamin-dependent enzyme, methionine synthase. S-adenosyl-L-methionine, known as SAMe, is the main biological donor of methyl groups and it has several important therapeutic applications. As a substance existing in the living body, SAMe has been found to possess various pharmacological actions such as improvement of energy state of ischemic brain, improvement of cerebral energy metabolism and acidosis of the model with recirculated blood flow following ischemia, etc. L-methionine can be prepared from natural sources such as casein hydrolyzate, by fermentation processes or by resolution of racemic methionine. Methionine deficiency is not recognized as a disease state in modern countries where adequate total protein is Generally available. Methionine is not recommended for persons being treated with monoamine oxidase inhibitors such as deprenyl.

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