Methionine

Methionine
Systematic name	(S)-2-Amino-4-(methyl- sulfanyl)butanoic acid
Abbreviations	Met M
Chemical formula	C₅H₁₁NO₂S
Molecular mass	149.21 g mol^-1
Melting point	281 °C
Density	1.340 g cm^-3
Isoelectric point	5.74
pK_a	2.16 9.08
CAS number	[63-68-3]
EINECS number	200-562-9
SMILES	C(N)(C(O)O)CCSC

Disclaimer and references

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

Methionine and cysteine are the only sulfur containing proteinogenic amino acids. The methionine derivative S-adenosyl methionine (SAM) serves as a methyl donor. Methionine 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.

File:Met-stick.png

Methionine is one of only two amino acids encoded by a single codon (AUG) in the standard genetic code (tryptophan, encoded by UGG, is the other). The codon AUG is also significant, in that it carries the "Start" message for a ribosome to begin protein translation from mRNA. Consequently, methionine is incorporated into the N-terminal position of all proteins in eukaryotes and archaea during translation, although it is usually removed by post-translational modification. Methionine can also occur at other positions in the protein.

Foods containing methionine include fruits, vegetables, and legumes. High levels of methionine can be found in spinach, green peas, corn, navel and mandarin oranges, peanuts, pistachios, macadamia nuts, kidney beans, black turtle beans, tofu, and tempeh.