title: Mechanism of oxygen activation by tyrosine hydroxylase.
abstract: The mechanism by which the tetrahydropterin-requiring enzyme tyrosine hydroxylase (TH) activates dioxygen for substrate hydroxylation was explored. TH contains one ferrous iron per subunit and catalyzes the conversion of its tetrahydropterin cofactor to a 4a-carbinolamine concomitant with substrate hydroxylation. These results are in accord with shared mechanisms of oxygen activation by TH and the more commonly studied tetrahydropterin-dependent enzyme phenylalanine hydroxylase (PAH) and strongly suggest that a peroxytetrahydropterin is the hydroxylating species generated during TH turnover. In addition, TH can also utilize H2O2 as a cofactor for substrate hydroxylation, a result not previously established for PAH. A detailed mechanism for the reaction is proposed. While the overall pattern of tetrahydropterin-dependent oxygen activation by TH and PAH is similar, the H2O2-dependent hydroxylation performed by TH provides an indication that subtle differences in the Fe ligand field exist between the two enzymes. The mechanistic ramifications of these results are briefly discussed.
mesh_terms: D000310:Adrenal Gland Neoplasms / Q000201:enzymology; D000818:Animals; D002460:Cell Line; D006900:Hydroxylation; D007700:Kinetics; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism*; D010673:Pheochromocytoma / Q000201:enzymology; D051381:Rats; D013050:Spectrometry, Fluorescence; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism*
chemical_list: D014446:Tyrosine 3-Monooxygenase; D010100:Oxygen