Mythionine

Methionine (Met, M. C5H11NO2S) is a essential nonpolar amino acid, and a lipotropic.

It and cysteine are the only sulfur containing amino acids that are coded for by DNA (Homocysteine is an amino acid and contains sulfur, but is a product of S-adenosylmethionine 1 carbon metabolism and is not coded for by DNA). Methionine is a methyl donor as S-adenosyl methionine (SAM). It is incorporated into the N-terminal position of all proteins in eukaryotes and archaea, though it may be removed by post-translational modification (bacteria incorporate N-formyl methionine instead). It plays a role in cysteine, carnitine and taurine synthesis by the transsulfuration pathway, lecithin production, the synthesis of phosphatidylcholine and other phospholipids. Improper conversion of methionine can lead to atherosclerosis. Methionine is a chelating agent.

Most amino acids have a redundant genetic code; several different nucleotide sequences code for the same amino acid, giving a degree of error-correction to the genetic sequence, usually with the third base in the codon being non-specific. Methionine is one of only two amino acids with a single codon, AUG. (Tryptophan, encoded by UGG, is the other)

What does methionine do?

Methionine is one of the essential amino acids (building blocks of protein), meaning that it cannot be produced by the body, and must be provided by the diet. It supplies sulfur and other compounds required by the body for normal metabolism and growth. Methionine also belongs to a group of compounds called lipotropics, or chemicals that help the liver process fats (lipids). Others in this group include choline, inositol, and betaine(trimethylglycine).

People with AIDS have low levels of methionine. Some researchers suggest this may explain some aspects of the disease process,1 2 3 especially the deterioration that occurs in the nervous system that can cause symptoms, including dementia.4 5 A preliminary study has suggested that methionine (6 grams per day) may improve memory recall in people with AIDS-related nervous system degeneration.6

Other preliminary studies have suggested that methionine (5 grams per day) may help treat some symptoms of Parkinson’s disease.7 However, another form of methionine, S-adenosylmethionine (SAMe) may worsen the symptoms of Parkinson’s disease and should be avoided until more is known.8 9 10 11 12

Methionine (2 grams per day) in combination with several antioxidants, reduced pain and recurrences of attacks of pancreatitis in a small but well-controlled trial.13

Where is methionine found?

Meat, fish, and dairy are all good sources of methionine. Vegetarians can obtain methionine from whole grains, but beans are a relatively poor source of this amino acid.

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Structure of Amino Acids
Amino Acid Properties

Classes of Amino Acids
Amino Acid Disorders Screening
Functions and Non-functions in proteins