''S''-Methylcysteine is the

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...

with the nominal formula CH₃SCH₂CH(NH₂)CO₂H. It is the S-methylated derivative of

cysteine Cysteine (; symbol Cys or C) is a semiessential proteinogenic amino acid with the chemical formula, formula . The thiol side chain in cysteine enables the formation of Disulfide, disulfide bonds, and often participates in enzymatic reactions as ...

. This amino acid occurs widely in plants, including many edible vegetables.

Natural occurrence

S-Methylcysteine is not genetically coded, but it arises by

post-translational In molecular biology, post-translational modification (PTM) is the covalent process of changing proteins following protein biosynthesis. PTMs may involve enzymes or occur spontaneously. Proteins are created by ribosomes, which translate mRNA int ...

methylation Methylation, in the chemistry, chemical sciences, is the addition of a methyl group on a substrate (chemistry), substrate, or the substitution of an atom (or group) by a methyl group. Methylation is a form of alkylation, with a methyl group replac ...

of cysteine. One pathway involves methyl transfer from alkylated DNA by zinc-cysteinate-containing repair enzymes such as methylated-DNA-protein-cysteine methyltransferase. S-Methylcysteine sulfoxide is an oxidized derivative of S-methylcysteine that is found in

onion An onion (''Allium cepa'' , from Latin ), also known as the bulb onion or common onion, is a vegetable that is the most widely cultivated species of the genus '' Allium''. The shallot is a botanical variety of the onion which was classifie ...

s. MetaCyc contains a list of biochemical reactions producing and consuming this substance.

Other chemical properties

Beyond its biological context, S-methylcysteine has been examined as a

chelating agent Chelation () is a type of bonding of ions and their molecules to metal ions. It involves the formation or presence of two or more separate coordinate bonds between a polydentate (multiple bonded) ligand and a single central metal atom. These l ...

References

{{DEFAULTSORT:Methylcysteine, S- Biochemistry Sulfur amino acids Thioethers Alpha-Amino acids Amino acid derivatives