Reversible and competitive inhibitory kinetics of amoxicillin on mushroom tyrosinase

Natural Science Foundation of China [31071611]; National Science Foundation for Fostering Talents in Basic Research of the National Natural Science Foundation of China [J1310027/J0106]; Science and Technology Foundation of Fujian Province [2010N5013]In the present work, we investigated the inhibitory effects of amoxicillin, a bacteriolytic beta-lactam antibiotic drug, on the rate of monophenol hydroxylation and o-diphenol oxidation catalyzed by mushroom tyrosinase. The results showed that amoxicillin could inhibit both monophenolase and diphenolase activities. For monophenolase activity, the inhibition on reaction rate was dose-dependent, while the influence on lag period was not obvious. For diphenolase activity, amoxicillin was found to be a reversible inhibitor, with an IC50 value of 9.0 +/- 1.8 mM. Kinetics analysis showed that amoxicillin was a mixed type inhibitor of the enzyme with K-I and K-IS values of 8.30 mM and 44.79 mM, respectively. Further, the molecular mechanism underlying the inhibition of tyrosinse by amoxicillin was investigated by means of fluorescence quenching and molecular docking techniques. The results showed that amoxicillin could form static interaction with the catalytic pocket of the enzyme through the interaction of amoxicillin with the dicopper irons and amino acid residues in the enzyme active center. Our results contributed to the usage of amoxicillin as a potential tyrosinase inhibitor in the field of medicinal industry and could also provide guidance in the design of novel tyrosinase inhibitors. (C) 2013 Published by Elsevier B.V