Kinetic study of the activation process of a latent mushroom (Agaricus bisporus) tyrosinase by serine proteases

Latent mushroom tyrosinase can be considered as a zymogen when activated by proteases because the activation process fulfilled all of the kinetic depe ndencies predicted by a theoretical zymogen activation model previously rep orted. The activation was studied under two assay conditions: high and low ratio of latent tyrosinase/serine protease (trypsin and subtilisin Carlsber g) concentrations, in the presence and in the absence of a serine protease inhibitor (aprotinin). The size of the latent enzyme was 67 kDa, determined by denaturing SDS-PAGE electrophoresis and Western blot assays. After prot eolytic activation, the size was 43 kDa, with an intermediate band of 58 kD a. The values of the catalytic (k(cat)(S)) and Michaelis (K-m(S)) constants for the active forms of tyrosinase resulting from the activation by subtil isin, trypsin, or sodium dodecyl sulfate on the substrate tert-butylcatecho l were slightly different, which could support the idea of "one activator-o ne different active tyrosinase". Vacuum infiltration experiments tried to r eproduce in vivo the role of mushroom serine proteases in the activation of latent tyrosinase. The use of serine protease inhibitors is proposed as a new alternative tool to prevent melanin formation.