Reaction mechanism to explain the high kinetic autoactivation of tyrosinase

The autoactivation of tyrosinase acting on monophenols has been quantitatively characterised by a new kinetic parameter, the rate autoactivation factor (RAF). This parameter is equivalent to the ratio between the initial and final steady-state rates of tyrosinase in its monophenolase activity. The experimental RAF data for l-tyrosine point to a kinetic behaviour with respect to the monophenol and enzyme concentrations, which coincides with the data obtained in numerical simulations of the kinetic reaction mechanism proposed for tyrosinase. Moreover, the experimental data are also in agreement with the expected dependencies obtained from the analytical expression of RAF, as described in this paper. These results establish the validity of the kinetic reaction mechanism proposed by us for tyrosinase, and confirm the melanogenesis pathway described in text books: tyrosine → dopa → dopaquinone → dopa + melanins → melanins.