Inhibitory effects of hinokitiol on tyrosinase activity and melanin biosynthesis and its antimicrobial activities.

The inhibitory effects of hinokitiol, a constituent of the woody oils isolated from Cupressaceae heartwood, on mushroom tyrosinase and melanin formation in B16 melanoma cells as well as its antimicrobial activity were investigated. Our results showed that hinokitiol could strongly inhibit both monophenolase activity and diphenolase activity of the enzyme and the inhibition was reversible. The IC(50) values were estimated as 9.67 µM for monophenolase activity and 0.21 µM for diphenolase activity. The lag time of the monophenolase activity was not obviously lengthened by the compound. Kinetic analyses showed that the inhibition mechanism of hinokitiol was a mixed-type inhibition of the diphenolase activity. Hinokitiol effectively inhibited both cellular tyrosinase activity and melanin biosynthesis in B16 melanoma cells with significant cytotoxicity. Furthermore, it was found that hinokitiol could inhibit the proliferation of Salmonella enteritidis, Escherichia coli, Bacillus subtilis, Staphyloccocus aureus, Klebsiella pneumoniae, and Ralstonia solanacearum to different extents. This research may widen the use of hinokitiol in the fields of food preservation, depigmentation, and insecticide use.

Inhibition effects of benzylideneacetone, benzylacetone, and 4-phenyl-2-butanol on the activity of mushroom tyrosinase.

Tyrosinase (EC 1.14.18.1) is the key enzyme of melanin synthesis and fruit-vegetable browning. The inhibition of benzylideneacetone, benzylacetone, and 4-phenyl-2-butanol on mushroom tyrosinase was first investigated. The results shown that these three compounds could effectively inhibit the enzyme activity sharply and the inhibitory effects were determined to be reversible. Their inhibitor concentrations leading to 50% activity lost values were determined to be 1.5, 2.8, and 1.1 mM for monophenolase and 2.0, 0.6, and 0.8 mM for diphenolase, respectively. For the monophenolase activity, all of these three compounds were mixed-type inhibitors, however, only 4-phenyl-2-butanol obviously lengthened the lag time. For the diphenolase activity, benzylideneacetone and benzylacetone were mixed-type inhibitors, while 4-phenyl-2-butanol was a noncompetitive type inhibitor. In conclusion, these compounds exhibited potent antityrosinase activities. This research would provide scientific evidence for the use of benzylideneacetone, benzylacetone, and 4-phenyl-2-butanol as antityrosinase agents.

Inhibitory effects of 4-halobenzoic acids on the diphenolase and monophenolase activity of mushroom tyrosinase.

The effects of 4-halobenzoic acids (4-fluorobenzoic acid, 4-chlorobenzoic acid, and 4-bromobenzoic acid) on the activity of mushroom tyrosinase have been studied. The results show that 4-halobenzoic acids can strongly inhibit both monophenolase activity and diphenolase activity of the enzyme, and the inhibition displays a reversible course. The IC50 values were estimated as 0.26, 0.20, and 0.18 mM for diphenolase activity and as 1.03, 0.75, and 0.60 mM for monophenolase activity, respectively. Kinetic analyses show that the inhibition mechanism of all three 4-halobenzoic acids is noncompetitive inhibition to the diphenolase activity, and the inhibition constants (K1) were determined to be 0.25, 0.20, and 0.17 mM, respectively. The lag time of the monophenolase was obviously lengthened by these three 4-halobenzoic acids. When the concentration of inhibitors reached 1.4 mM, the lag time was lengthened from 30 s to 120, 125, and 150 s, respectively.