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DL-Methionine is an essential amino acid in humans. As the precursor of other amino acids such as cysteine and taurine, versatile compounds such as SAM-e, and the important antioxidant glutathione, methionine plays a critical role in the metabolism and health of many species, including humans. It is encoded by the codon AUG.
Methionine is also an important part of angiogenesis, the growth of new blood vessels. Supplementation may benefit those suffering from copper poisoning. Overconsumption of methionine, the methyl group donor in DNA methylation, is related to cancer growth in a number of studies.Methionine was first isolated in 1921 by John Howard Mueller
Methionine (abbreviated as Met or M; encoded by the codon AUG) is an α-amino acid that is used in the biosynthesis of proteins. It contains a carboxyl group (which is in the deprotonated −COO− form under biological pH conditions), an amino group (which is in the protonated −NH3+ form under biological pH conditions) located in α-position with respect to the carboxyl group, and an S-methyl thioether side chain, classifying it as a nonpolar, aliphatic amino acid.
High levels of methionine can be found in eggs, meat, and fish; sesame seeds, Brazil nuts, and some other plant seeds; and cereal grains. Most fruits and vegetables contain very little. Most legumes, though protein dense, are low in methionine. Proteins without adequate methionine are not considered to be complete proteins.For that reason, racemic methionine is sometimes added as an ingredient to pet foods.
The Food and Nutrition Board of the U.S. Institute of Medicine set Recommended Dietary Allowances (RDAs) for essential amino acids in 2002. For methionine combined with cysteine, for adults 19 years and older, 19 mg/kg body weight/day. This translates to about 1.33 grams per day for a 70 kilogram individual.
|Molar mass||149.21 g·mol−1|
|Appearance||White crystalline powder|
|Density||2.929 g/cm3 (anhydrous)|
|Melting point||281 °C (538 °F; 554 K) decomposes|
|Solubility in water||Soluble|