Lysine's secret

[Corakus]

Lysine (symbol Lys or K) is an α-amino acid that is a precursor to many proteins. It consists of an α-amino group (in the −NH+3 form, protonated when dissolved in water), an α-carboxylic acid group (in the −COO− form, deprotonated when dissolved in water), and a lysyl side chain ((CH2)4NH2). It is an aliphatic amino acid with a basic charge (at physiological pH). It is encoded by the codons AAA and AAG. Like almost all other amino acids, the α-carbon is chiral, and lysine can refer to its enantiomer or to a racemic mixture of the two. For the purposes of this article, lysine will refer to the biologically active enantiomer L-lysine, in which the α-carbon is in the S form.

The human body cannot synthesize lysine; it is essential in humans and must be obtained from the diet. Two main biosynthetic pathways exist in organisms that synthesize lysine: the diamino pimelate and α-amino adipate pathways, which use different enzymes and substrates and are found in a wide variety of organisms. Lysine catabolism occurs through one of several pathways, the most common of which is the saccharin pathway.

Lysine has many roles in humans, the most important of which is protein synthesis, but also in the cross-linking of collagen polypeptides, the absorption of essential mineral nutrients, and the production of carnitine, which is key to fatty acid metabolism. Lysine is also frequently involved in histone modifications and, as such, affects the epigenome. The ε-amino group is often involved in hydrogen bonding and is a common base for catalysis. The ε-ammonium group (−NH+3) is attached to the fourth carbon from the α-carbon, which is attached to the carboxyl group (−COOH).