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 (lambda(max) = 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).