Isotope effects in the hydroxylation of l-tyrosine catalyzed by tyrosinase

Abstract

The reaction mechanism of the enzymatic hydroxylation of l-tyrosine (l-Tyr) to l-DOPA catalyzed by enzyme tyrosinase (EC 1.14.18.1) were investigated using the kinetic (KIE) and solvent (SIE) isotope effect methods. The values of deuterium KIE’s and SIE’s for [2′,6′-²H₂]-, and [3′,5′-²H₂]-l-Tyr were obtained using a non-competitive spectrophotometric method but values of H/T and D/T KIE’s for the 3′- and 5′-positions of [3′,5′-³H₂]-, and [3′,5′-²H/³H]-l-Tyr were determined by competitive method with [1-¹⁴C]-l-Tyr as internal radioactive standard.