The effect of pH on the suicide inactivation of frog epidermis tyrosinase

Abstract

This paper presents a new reaction mechanism for the effect of the pH on the suicide inactivation of the diphenolase activity of tyrosinase. The applicability of the mechanism is supported by the experimental characterization of the kinetic behaviour of the frog epidermis enzyme acting on catechol, l-dopa and α-methyldopa at several pH values. Two enzyme forms ‘met-’ and ‘oxy-’ tyrosinase, but no their corresponding enzyme-diphenol complexes, present one ionizable group with very similar value of K a which has been determined. The highest values of catalytic and inactivation efficiencies correspond to α-methyldopa and catechol, respectively. These kinetic studies have been carried out by using the transient phase approach previously developed, with negligible substrate consumption during the assay time. That illustrate the usefulness of the method for multisubstrate enzyme reactions.