Inhibition kinetics of chlorobenzaldehyde thiosemicarbazones on mushroom tyrosinase.

2-Chlorobenzaldehyde thiosemicarbazone (2-Cl-BT) and 4-chlorobenzaldehyde thiosemicarbazone (4-Cl-BT) were synthesized, and their inhibitory kinetics on the activity of mushroom tyrosinase were investigated. Results showed that these compounds exhibited significant inhibitory potency on both monophenolase activity and diphenolase activity of tyrosinase. For the monophenolase activity, both compounds could decrease the steady-state activity of the enzyme sharply, without any influence on the lag period. The IC50 values of them were estimated to be 15.4 μM and 6.7 μM, respectively. For the diphenolase activity, both compounds belonged to reversible inhibitors, but their mechanisms were different: 2-Cl-BT was a noncompetitive type inhibitor, while 4-Cl-BT was a mixed-type inhibitor. Their inhibition constants were determined and compared.