4382 L-Methionine Methionine is a dietary indispensable amino acid required for normal growth and development of humans, other mammals, and avian species. In addition to being a substrate for protein synthesis, it is an intermediate in transmethylation reactions, serving as the major methyl group donor in vivo, including the methyl groups for DNA and RNA intermediates. Methionine is a methyl acceptor for 5-methyltetrahydrofolate-homocysteine methyl transferase (methionine synthase), the only reaction that allows for the recycling of this form of folate, and is also a methyl acceptor for the catabolism of betaine. Methionine is also required for synthesis of cysteine. Methionine is accepted as the metabolic precursor for cysteine. Only the sulfur atom from methionine is transferred to cysteine; the carbon skeleton of cysteine is donated by serine. The adequacy range of dietary requirements of specific amino acids in disease states is difficult to determine. Requirements may not be similar in disease with regard to protein synthesis. Requirements for this purpose can be assessed only when such a function can be measured and related to clinical outcome. There is apparent consensus concerning normal sulfur amino acid (SAA) requirements. WHO recommendations amount to 13 mg/kg per 24 h in healthy adults. This amount is roughly doubled in artificial nutrition regimens. In disease or after trauma, requirements may be altered for methionine, cysteine, and taurine. Although in specific cases of congenital enzyme deficiency, prematurity, or diminished liver function, hypermethionemia or hyperhomocysteinemia may occur, SAA supplementation can be considered safe in amounts exceeding 2-3 times the minimal recommended daily intake. Apart from some very specific indications (e.g., acetaminophen poisoning) the usefulness of SAA supplementation is not yet established. Methionine is known to exacerbate psychopathological symptoms in schizophrenic patients, there is no evidence of similar effects in healthy subjects. The role of methionine as a precursor of homocysteine is the most notable cause for concern. A loading dose of methionine (0.1 g/kg) has been given, and the resultant acute increase in plasma homocysteine has been used as an index of the susceptibility to cardiovascular disease. Although this procedure results in vascular dysfunction, this is acute and unlikely to result in permanent damage. However, a 10-fold larger dose, given mistakenly, resulted in death. Longer-term studies in adults have indicated no adverse consequences of moderate fluctuations in dietary methionine intake, but intakes higher than 5 times normal resulted in elevated homocysteine levels. These effects of methionine on homocysteine and vascular function are moderated by supplements of vitamins B-6, B-12, C, and folic acid. In infants, methionine intakes of 2 to 5 times normal resulted in impaired growth and extremely high plasma methionine levels, but no adverse long-term consequences were observed. (A3417, A3418, A3419). It is a chelating agent for heavy metals. 63-68-3 6137 C5H11NO2S 149.21 White powder. 283 dec°C 5.66E+004 mg/L (at 25°C) Absorbed from the lumen of the small intestine into the enterocytes by an active transport process. The mechanism of the possible anti-hepatotoxic activity of L-methionine is not entirely clear. It is thought that metabolism of high doses of acetaminophen in the liver lead to decreased levels of hepatic glutathione and increased oxidative stress. L-methionine is a precursor to L-cysteine. L-cysteine itself may have antioxidant activity. L-cysteine is also a precursor to the antioxidant glutathione. Antioxidant activity of L-methionine and metabolites of L-methionine appear to account for its possible anti-hepatotoxic activity. Recent research suggests that methionine itself has free-radical scavenging activity by virtue of its sulfur, as well as its chelating ability. Hepatic No indication of carcinogenicity to humans (not listed by IARC). Used for protein synthesis including the formation of SAMe, L-homocysteine, L-cysteine, taurine, and sulfate. Chronically high levels of methionine are associated with at least 7 inborn errors of metabolism including: Cystathionine Beta-Synthase Deficiency, Glycine N-methyltransferase Deficiency, Homocystinuria-megaloblastic anemia due to defect in cobalamin metabolism, Methionine Adenosyltransferase Deficiency, Methylenetetrahydrofolate reductase deficiency and S-Adenosylhomocysteine (SAH) Hydrolase Deficiency. 2014-08-29T06:27:43Z 2026-05-14T16:24:10Z MET C01733 16643 MET DB00134 MET true CSCC[C@H](N)C(O)=O C5H11NO2S InChI=1S/C5H11NO2S/c1-9-3-2-4(6)5(7)8/h4H,2-3,6H2,1H3,(H,7,8)/t4-/m0/s1 FFEARJCKVFRZRR-BYPYZUCNSA-N 149.211 149.051049291 Endogenous Solid -1.87 HMDB00696 CHEMBL42336 5907 <p>Clyde Eugene Stauffer, &#8220;Process for producing N-acyl-L-methionine.&#8221; U.S. Patent US3963573, issued June, 1950.</p> CHEM003288 DTXSID5040548 (2S)-2-amino-4-(methylsulfanyl)butanoic acid 63.31999999999999 37.586000000000006 15.504513637142049 4 3 2 2.5319210041042344 9.502323343916569 0 0 -1.85 -0.80 2.39e+01 g/l