Tyrosinase kinetics: A semi-quantitative model of the mechanism of oxidation of monohydric and dihyric phenolic substrates

A mathematical model of phase I melanogenesis is described based on the differential reactivity of tyrosinase according to the redox status of the active site copper atoms shown by Lerch and co-workers (see Lerch, 1981, Metal Ions in Biological Systems (Sigel, H., ed.) Vol. 13, pg. 143-186. New York: Marcel Dekker) in combination with the indirect formation of the catecholic intermediate substrate. In this model the unusual autoactivation kinetics of tyrosinase are explained by recruitment of enzyme from the met-form, in which the active-site copper atoms are in the oxidized (Cu(II)) state, by 2-electron donation from catechol oxidation. Using estimates of the values for the rate-constants of the six reactions involved, the general characteristics of the model are shown to be consistent with the kinetic behaviour of tyrosinase in vitro. These include a lag period which is sensitive to catechol addition. (C) 2000 Academic Press.