Identification and discrimination between some contaminant enzyme activities in commercial preparations of mushroom tyrosinase

Tyrosinase is a copper-enzyme involved in important biological processes. Many studies investigating these topics have relied on commercial preparations of mushroom tyrosinase as a tool or use as a model system. In this study, several commercial preparations of tyrosinase have been examined with regard to their composition and purity. Enzyme activities different from tyrosinase were found. Laccase, β-glucosidase, β-xylosidase, and xylanase activities were found in almost all samples examined. In particular, laccase and β-glucosidase were investigated for their ability to affect tyrosinase activity under certain experimental conditions. Laccase activity was variable in different commercial preparations and its presence could lead to misinterpretation of results ascribed to tyrosinase activity. In fact, it could hide the inhibitory effect of tropolone and kojic acid in relation to tyrosinase activity. β-Glucosidase released the aglycon moiety from the glucoside esculin which in turn could become a tyrosinase inhibitor or substrate. SDS–PAGE of commercial mushroom tyrosinase showed a complex pattern of unidentified proteins with at least four major and many minor protein staining bands. Taken together, these findings confirm that investigators should use caution in interpreting data relying on commercial sources of mushroom tyrosinase.