Isolation of Sulfuretin and Butin from Rhus verniciflua Stokes Using Medium-pressure Liquid Chromatography and their Tyrosinase Inhibitory Effects

The aim of this study was to separate antityrosinase compounds of the ethyl acetate fraction from Rhus verniciflua Stokes using medium pressure liquid chromatography. Among the different fractions, the Fr.6 fraction showed the highest antityrosinase capacity (96.5%), followed by the Fr.5 fraction (85.6%). The Fr.1 fraction showed the lowest antityrosinase capacity (12.4%). Bioactivity-guided fractionation of Fr.5.5 and Fr.6.4 led to the isolation and identification of butin and sulfuretin. Then the inhibitory effects of butin and sulfuretin on the monophenolase and diphenolase activity of mushroom tyrosinase were investigated. The results showed that butin and sulfuretin can act as potent inhibitors of monophenolase and diphenolase activities of the enzyme, and the IC50 of the butin and sulfuretin were 16.0 μmol/L and 13.64 μmol/L, respectively. The lag period of the enzyme was obviously lengthened; it was estimated to be 1 min in the absence of inhibitor, extended to 26 min in the presence of 185 μmol/L of butin, and 6 min in the presence of 111.1 μmol/L of sulfuretin. A kinetic analysis showed that butin and sulfuretin are competitive inhibitors. The results revealed that the butin and sulfuretin took up the loci of the substrate combined with enzyme, or blocked the anionic initiation by eliminating free radicals, thus weakening the catalytic reaction of oxidation of L-dopa.