Tyrosine hydroxylase (TH), also designated tyrosine 3-monooxygenase (TY3H), catalyzes the rate-limiting step in the synthesis of the neurotransmitter dopamine and other catecholamines, hence plays a key role in the physiology of adrenergic neurons. TH functions as a tetramer, with each subunit composed of a regulatory and catalytic domain, and exists in several different isoforms. TH is thought to play a role in the pathogenesis of Parkinson’s disease, which is associated with reduced dopamine levels. The amino-terminal regulatory domain contains three serine residues: Ser9, Ser31 and Ser40. Levels of transcription, translation and posttranslational modification regulate TH activity.
