Native and Phosphorylated Bovine Adrenal Tyrosine 3-Monooxygenase. Interactions with Tetrahydropterins and Substrate and Stability of the Formed 4a-Hydroxy-Tetrahydrobiopterin

Abstract

The catalytic activity of tyrosine 3-monooxygenase (tyrosine hydroxylase) is dependent on a tetrahydropterin cofactor and ezyme-bound iron. The oxidation of tetrahydrobiopterin by bovine adrenal tyrosine hydroxylase was studied by high performance liquid chromatography (HPLC). The first pterin product detected during catalytic turnover, 4a-hydroxy-tetrahydrobiopterin, was isolated by HPLC and the pseudo first-order rate constant of its dehydration to quinonoid dihydrobiopterin was estimated. The tl /2 was found to be 45 and 72 s in 100 and 5 mmol/L Tris-HCl, respectively, at pH 7.5 and 23 °C.