Methionine

Methionine

Canonical form of methionine
Resonance line-angle diagram of L-methionine at physiological pH
Names
IUPAC name Methionine
Other names 2-amino-4-(methylthio)butanoic acid
Identifiers
CAS Number	59-51-8 Y 63-68-3 (L-isomer) Y 348-67-4 (D-isomer) Y
3D model (Jmol)	Interactive image Interactive image
Abbreviations	Met, M
ChEBI	CHEBI:16811 Y
ChEMBL	ChEMBL42336 N
ChemSpider	853 Y 5907 (L-isomer) Y
ECHA InfoCard	100.000.393
EC Number	200-432-1
KEGG	D04983 Y
PubChem	876
UNII	73JWT2K6T3 Y
InChI InChI=1S/C5H11NO2S/c1-9-3-2-4(6)5(7)8/h4H,2-3,6H2,1H3,(H,7,8) Y Key: FFEARJCKVFRZRR-UHFFFAOYSA-N Y InChI=1/C5H11NO2S/c1-9-3-2-4(6)5(7)8/h4H,2-3,6H2,1H3,(H,7,8)
SMILES CSCCC(C(=O)O)N CSCCC(C(=O)O)N
Properties
Chemical formula	C5H11NO2S
Molar mass	149.21 g·mol−1
Appearance	White crystalline powder
Density	1.340 g/cm3
Melting point	281 °C (538 °F; 554 K) decomposes
Solubility in water	Soluble
Acidity (pKa)	2.28 (carboxyl), 9.21 (amino)
Pharmacology
ATC code	V03AB26 (WHO) QA05BA90 (WHO), QG04BA90 (WHO)
Supplementary data page
Structure and properties	Refractive index (n), Dielectric constant (εr), etc.
Thermodynamic data	Phase behaviour solid–liquid–gas
Spectral data	UV, IR, NMR, MS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YN ?)
Infobox references

Methionine is an essential amino acid in humans. Methionine is important in angiogenesis, the growth of new blood vessels, and supplementation may benefit those suffering from Parkinson's, drug withdrawal, schizophrenia, radiation, copper poisoning, asthma, allergies, alcoholism, or depression. Overconsumption of methionine, as is typical in the standard American diet, but not vegan diet (although nuts, soy, and beans also have high levels of methionine), 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 an α-amino group (which is in the protonated −NH₃⁺ form under biological conditions), an α-carboxylic acid group (which is in the deprotonated −COO⁻ form under biological conditions), and an S-methyl thioether side chain, classifying it as a non-polar, aliphatic amino acid.

Methionine is coded for by the initiation codon, meaning it indicates the start of the coding region and is the first amino acid produced in a nascent polypeptide during mRNA translation.

Together with cysteine, methionine is one of two sulfur-containing proteinogenic amino acids. Excluding the few exceptions where methionine may act as a redox sensor (e.g. ), methionine residues do not have a catalytic role. This is in contrast to cysteine residues, where the thiol group has a catalytic role in many proteins. The thioether does however have a minor structural role due to the stability effect of S/π interactions between the side chain sulfur atom and aromatic amino acids in one-third of all known protein structures. This lack of a strong role is reflected in experiments where little effect is seen in proteins where methionine is replaced by norleucine, a straight hydrocarbon sidechain amino acid which lacks the thioether. It has been conjectured that norleucine was present in early versions of the genetic code, but methionine intruded into the final version of the genetic code due to the fact it is used in the cofactor S-adenosyl methionine (SAM). This situation is not unique and may have occurred with ornithine and arginine.