Accession NumberHMDB00696
Common_NameL-Methionine
DescriptionMethionine 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. (PMID 16702340) 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.(PMID 16702341) 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. (PMID 16702346)
Chemical_IUPAC_Name(2S)-2-amino-4-methylsulfanyl-butanoic acid
Chemical FormulaC5H11NO2S
Sample Concentration1
Mass ValueNot Available
Mass Unitmg
ManufacturerQuattro_QQQ
AnalyzerTriple_Quad
DeliveryFlow_Injection
IonizationPositive
Predicted 1H NMR SpectrumDownload
Predicted 1H NMR PeaklistDownload
Predicted 13C NMR SpectrumDownload
Predicted 13C NMR PeaklistDownload
Sample ConcentrationNot Available
Mass ValueNot Available
Mass UnitNot Available
ManufacturerNot Available
FrequencyNot Available
1H NMR Spectrum
Sample ConcentrationNot Available
Mass ValueNot Available
Mass UnitNot Available
ManufacturerNot Available
FrequencyNot Available
13C NMR Spectrum
Low Energy Voltage10
Low Energy SpectrumDownload
Low Energy PeaklistDownload
Medium Energy SpectrumDownload
High Energy SpectrumDownload