EFFECT OF KOJIC ACID ON THE OXIDATION OF N-ACETYLDOPAMINE BY MUSHROOMTYROSINASE

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 act ivity). Kojic acid had a pronounced effect on the spectrum of product( s) obtained when NADA was oxidized by mushroom tyrosinase. In its abse nce, NADA quinone (lambda(max) = 390 +/- 10 nm) was formed; in its pre sence, a stable final yellow product(s), characterized by a peak at 34 0 +/- 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).