Tyrosine hydroxylase is a member of the aromatic amino acid hydroxylase (AAAH) family. It is expressed throughout the central nervous system (CNS) and catalyzes the conversion of tyrosine to L-3,4-dihydroxyphenylalanine (L-DOPA), which can be, through a series of downstream enzymatic reactions, processed into the neurotransmitter and signaling molecule dopamine. Dopamine can then be further altered to produce norepinephrine or epinephrine.
In the synthesis pathway for the catecholamines - dopamine, epinephrine, and norepinephrine, tyrosine hydroxylase is the rate-limiting enzyme. Through alternative mRNA splicing, a wide molecular diversity of TH isoforms are generated that are tissue-specific and carry varied enzymatic activities, allowing for differential neurotransmitter availability at various synapses.
