Abstract
The mechanism of bleaching effects hydroquinone and its derivatives in melanin formation was investigated with manometric and spectrometric procedures. Tyrosinase was prepared from Harding-Passey mouse melanoma and either L-tyrosine or L-dopa was used as a substrate. Surprisingly, it was found with a manometric procedure that hydroquinone accelerated the oxygen consumption in a dopa-tyrosinase system, while it inhibited O2-uptake in tyrosine-tyrosinase system. However, the final solution of the dopa-tyrosinase system with hydroquinone or its derivatives did not darken, and remained reddish brown in color, showing inhibitory effects of hydroquinone on melanogenesis. Moreover, a spectrometric procedure revealed that hydroquinone itself was oxidized through p-quinone to another compound by tyrosinase. There is a general agreement that the tyrosinase has two different activities, that is, cresolase and catecholase. These contradictory results, thus, would be interpreted that hydroquinone blocked the tyrosine hydroxylase phase of tyrosinase, coupling with tyrosinase directory in a tyrosine-tyrosinase system, while it did not block the dopa oxidase phase of tyrosinase, competing with L-dopa in a dopa-tyrosinase system.
