Generation Mechanism of Radical Species by Tyrosine-Tyrosinase Reaction

Alleviated melanin formation in the skin through inhibition of tyrosine-tyrosinase reaction is one of the major targets of cosmetics for whitening ability. Since melanin has a pivotal role for photoprotection, there are pros and cons of inhibition of melanin formation. This study applying electron spin resonance (ESR)-spin trapping method revealed that H-center dot and (OH)-O-center dot are generated through tyrosine-tyrosinase reaction. When deuterium water was used instead of H2O, the signal of 5,5-dimethyl-1-pyrroline N-oxide (DMPO)-H (a spin adduct of DMPO and H-center dot) greatly decreased, whilst DMPO-OH (a spin adduct of DMPO and (OH)-O-center dot) did not. Thus, it is suggested that H-center dot was derived from H2O, and (OH)-O-center dot through oxidative catalytic process of tyrosine to dopaquinone. Our study suggests that tyrosinase inhibitors might contribute to alleviate the oxidative damage of the skin by inhibiting (OH)-O-center dot generation via the enzyme reaction.