TH (Tyrosine 3-hydroxylase), also known as Tyrosine 3-monooxygenase, is a 60-62 kDa member of the biopterin-dependent aromatic amino acid hydroxylase family of molecules. It is expressed by neurons of the dopamine and autonomic nervous system, plus the neuroendocrine cells of the adrenal medulla. TH is considered the rate limiting enzyme for catecholamine synthesis, and serves to catalyze the hydroxylation of L-tyrosine.
