Inhibitory kinetics of DABT and DABPT as novel tyrosinase inhibitors.

4-Dimethylaminobenzaldehyde-thiosemicarbazone (DABT) and 4-dimethylaminobenzaldehyde-N-phenyl-thiosemicarbazone (DABPT) were synthesized and established by (1)H and (13)C NMR and mass spectrum. Both compounds were evaluated for their inhibition activities on mushroom tyrosinase and their anti-tyrosinase kinetics was investigated. The results showed that both compounds exhibited significant inhibitory effects on activity of monophenolase and diphenolase; DABT and DABPT decreased the steady-state rate with 1.54 μM and 1.78 μM as their IC50 values respectively. The inhibitory effects of diphenolase activity exhibited sharp in a dose-dependent manner and their IC50 values were estimated as 2.01 μM and 0.80 μM, respectively. Kinetic analysis showed that their inhibition mechanism was reversible. The inhibition type of DABT was mix-type with inhibition constants KI = 1.77 μM and KIS = 6.49 μM, while that of DABPT displays non-competitive with the inhibition constant KI = 0.77 μM.