Inhibitory Effect of the Ethyl Acetate Fraction of Ethanol Extract from Rhus verniciflua Stokes Wood on the Activity of Mushroom Tyrosinase

Solvent extracts of Rhus verniciflua Stokes wood were made using decompressing inner ebullition, and a Box-Behnken design was used to optimize extraction conditions to produce an extract that inhibited tyrosinase activity. The chemical compositions and inhibition rates were determined in extracts made with petroleum ether, ethyl acetate, n-butanol, and an aqueous fractionation. The ethyl acetate fraction had the highest total phenolic content and inhibition rates. The main flavonoids in this fraction were 0.531% fisetin, 7.582% fustin, 0.848% sulfuretin, and 0.272% butein. The effects of the extract on the monophenolase and diphenolase activity of mushroom tyrosinase were studied using the Lineweaver-Burk equation to determine the effect of the extract on inhibition of tyrosinase activity. The results showed that the extract inhibited both the monophenolase and diphenolase activity of the enzyme. The IC50 of the ethyl acetate extract was 308 μg/mL, with the lag period of the enzyme being obviously lengthened; it was estimated to be 2.45 min in the absence of the inhibitor and extended to 9.63 min in the presence of 500 μg/mL of extract. The ethyl acetate extract acted as a mixed type inhibitor. The KI was less than the KIS, which demonstrates that the [ESI] is less stable than [EI], suggesting that the extract could easily combine with free enzyme in the enzyme catalysis system, thus affecting enzyme catalysis on the substrate.