tyrosine

Tyrosine (abbreviated as Tyr or Y) or 4-hydroxyphenylalanine, is one of the 22 amino acids that are used by cells to synthesize proteins. Its codons are UAC and UAU.

It is a non-essential amino acid with a polar side group. It is called tyrosyl when referred to as a functional group or side chain.

Aside from being a proteinogenic amino acid, tyrosine has a special role by virtue of the phenol functionality. It occurs in proteins that are part of signal transduction processes. It functions as a receiver of phosphate groups that are transferred by way of protein kinases. Phosphorylation of the hydroxyl group changes the activity of the target protein.