Intrinsic deuterium isotope effects on benzylic hydroxylation by tyrosine hydroxylase.

Journal of the American Chemical Society

PubMedID: 11960436

Frantom PA, Pongdee R, Sulikowski GA, Fitzpatrick PF. Intrinsic deuterium isotope effects on benzylic hydroxylation by tyrosine hydroxylase. J Am Chem Soc. 2002;124(16):4202-3.
Tyrosine hydroxylase (TyrH) is a mononuclear, non-heme iron monooxygenase that catalyzes the pterin-dependent hydroxylation of tyrosine to dihydroxyphenylalanine. When 4-methylphenylalanine is used as a substrate for TyrH, 4-hydroxymethylphenylalanine is one of the amino acid products. To examine the mechanism of benzylic hydroxylation, the products and their isotopic compositions were determined with 4-methylphenylalanines containing a mono-, di-, or trideuterated methyl group as substrates. Intrinsic primary and secondary deuterium isotope effects for benzylic hydroxylation of 9.6 +/- 0.9 and 1.21 +/- 0.08, respectively, were derived from the data. The magnitudes of these isotope effects are consistent with quantum mechanical tunneling of the hydrogen. The similarity of the effects to those seen for benzylic hydroxylation by other enzymes supports a mechanism where a high valence iron-oxo species, Fe(IV)=O, is the hydroxylating intermediate.