화학공학소재연구정보센터
Biochemical and Biophysical Research Communications, Vol.312, No.3, 642-649, 2003
Tyrosinase scavenges tyrosyl radical
Melanosomes scavenged tyrosyl radical that was generated by ultraviolet irradiation of tyrosine. Purified mushroom tyrosinase also removed tyrosyl radical in a dose-dependent manner. To elucidate the underlying mechanism, we analyzed the reaction of mushroom tyrosinase with tyrosyl radical generated by horseradish peroxidase and hydrogen peroxide. Resting tyrosinase, which contained a small amount of oxytyrosinase, did not oxidize tyrosine to DOPAchrome until horseradish peroxidase exhausted H2O2 and thereafter the enzyme recovered its full activity. During the inhibition period most tyrosine was converted to dityrosine, suggesting that only a small amount of tyrosyl radical was enough to interact with a fraction of tyrosinase which was in the active oxy-form. When horseradish peroxidase and H2O2 were added to oxytyrosinase, which was prepared by allowing it to turn over beforehand, DOPAchrome production was abolished with an accelerated consumption of H2O2. Dityrosine formation was totally suppressed and tyrosine concentration stayed constant during the inhibition period with a concomitant production of O-2 The results are accounted for by a mechanism in which tyrosyl radical is reduced to tyrosine by oxytyrosinase and the resulting met-form reacts with H2O2 to return to the oxy-form. (C) 2003 Elsevier Inc. All rights reserved.