Tyrosine hydroxylase (TH) is the first enzyme in catecholamine biosynthesis, as well as being the rate-limiting enzyme in that process. TH requires tetrahydrobiopterin and uses iron as a cofactor in the 3,4-hydroxylation of tyrosine to produce dopa. Four isoforms of TH are expressed in the human brain and all have enzymatic activity (Nagatsu, T, 1989; Lewis, DA et al, 1993).
Lewis, DA, Haycock, JW, Melchitzky, DS
tyrosine 3-monooxygenase activity of TH:Fe2+ [cytosol]
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