Hematoxylin, an Alternative Substrate of Tyrosinase.

Mushroom tyrosinase from Agaricus bisporus ( ab TYR) is often used during the development of tyrosinase inhibitors for medicinal and cosmetic purposes. In the search for novel tyrosinase inhibitors, this study identified hematoxylin as an alternative substrate for ab TYR. The interaction of hematoxylin with ab TYR was investigated through spectrophotometric and chromatographic analyses. The results showed that hematoxylin acted as an ab TYR substrate and exhibited Michaelis-Menten kinetic behaviour at concentrations below 1.25 mM. The substrate properties of hematoxylin were similar to the natural tyrosinase substrate, L-3,4-dihydroxyphenylalanine (L-DOPA), with regards to K m , while V max was eightfold lower. The main oxidation product formed during the reaction of ab TYR with hematoxylin was identified as hematein. This is the first report of the interaction of hematoxylin with ab TYR.