Tyrosinase scavenges tyrosyl radical

초록

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 H<inf>2</inf>O<inf>2</inf> 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 H <inf>2</inf>O<inf>2</inf> were added to oxytyrosinase, which was prepared by allowing it to turn over beforehand, DOPAchrome production was abolished with an accelerated consumption of H<inf>2</inf>O<inf>2</inf>. Dityrosine formation was totally suppressed and tyrosine concentration stayed constant during the inhibition period with a concomitant production of O<inf>2</inf>. 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 H <inf>2</inf>O<inf>2</inf> to return to the oxy-form. © 2003 Elsevier Inc. All rights reserved.

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