| Abstract: | Dihydroxybenzoic acids (DBA), such as 3,4-DRA, 3,5-DBA, and 2,4-DBA—at all concentrations tested—inhibited the rate of DL-DOPA oxidation to dopachrome (λmax = 475 nm) by mushroom tyrosinase. 2,3-DBA and 2,5-DBA at relatively low concentration had a synergistic effect on the reaction, whereas at relatively high concentrations they inhibited the rate of DL-DOPA oxidation. The synergistic effect of 0.6-13.3 mM 2,3-DRA on the rate of DL-DOPA oxidation to dopachrome (λmax = 475 nm) was found to be due to the ability of 2,3-DBA-o-quinone (formed by the oxidation of 2,3-DBA by mushroom tyrosinase or by sodium periodate) to oxidize DL-DOPA to dopachrome (via dopaquinone) non-enzymatically. A similar explanation is likely to be valid for the synergism exerted by 2,5-DBA on the rate of DL-DOPA oxidation by mushroom tyrosinase. |
