Kinetics study of the oxidation of 4‐tert‐butylphenol by tyrosinase

Abstract

The reaction between 4‐tert‐butylphenol (BuPhOH) and mushroom tyrosinase was investigated by following 4‐tert‐butyl‐ortho‐benzoquinone, whose high stability permits the reaction to be used as a model for the study of the monophenolase acfivity of tyrosinase. The system evolves to a pseudo‐steady state through an induction period (τ), the pseudo‐steady‐state rate (Vss) decreasing when the (BuPhOH) concentration increases. Increases in enzyme concentration result in a parabolic pattern with Vss, while τ is shortened. The addition of increasing catalytic amounts of 4‐tert‐butylcatechol at the start of the reaction reduces τ until it is totally abolished, an initial burst being observed at high 4‐t‐butylatechol concentrations. Initial bursts are also obtained at pH 4.5 or lower, indicating a lower affinity of the met‐tyrosinase or oxidized form for the monophenol at low pH. These experimental results can be explained by the reaction mechanism of tyrosinase. Copyright © 1994, Wiley Blackwell. All rights reserved