Effect of Kojic Acid on the Oxidation of N-Acetyldopamine by Mushroom Tyrosinase

Kojic acid inhibited mushroom tyrosinase, as judged by the inhibition it exerted on the rate of oxygen uptaked during N-acetyldopamine (NADA) oxidation. Preincubation of mushroom tyrosinase with kojic acid did not result in the inactivation of the enzyme (irreversible loss of activity). Kojic acid had a pronounced effect on the spectrum of product(s) obtained when NADA was oxidized by mushroom tyrosinase. In its absence, NADA quinone (λmax = 390 ± 10 nm) was formed; in its presence, a stable final yellow product(s), characterized by a peak at 340 ± 20 nm, was obtained. A maximum level of the final yellow product(s) was formed when the ratio between NADA quinone and kojic acid was 1:1. Spectral data suggest that NADA quinone oxidizes kojic acid to the yellow product(s). Keywords: N-Acetyldopamine (NADA); mushroom tyrosinase; kojic acid inhibition