TYROSINASE INHIBITORS FROM P. SUFFRUTICOSA 351 this study. One tannin compound pentagalloyl-β-D-glucose (VI) exhibited the most po- tent inhibitory activity toward mushroom tyrosinase among the six inhibitors purifi ed from the root of P. suffruticosa. Its inhibitory activity (IC50 value 0.063 mM) was slightly higher than that of kojic acid (IC50 value 0.070 mM). In addition, the compound’s inhi- bition kinetics was analyzed by the Lineweaver-Burk plot method, and the results are shown in Figure 2. The three lines, obtained from the uninhibited enzyme and the two concentrations of the inhibitor, intersect on the horizontal axis. These results demonstrate that pentagalloyl-β-D-glucose (VI) exhibited non-competitive inhibition of the oxidation of L-Dopa catalyzed by mushroom tyrosinase. P. suffruticosa is an important Chinese traditional medicine and acts as an antibiotic and a hemorrhage inhibitor. The present study identifi ed six tyrosinase inhibitors from the plant’s roots. Among them, the newly identifi ed tyrosinase inhibitor, pentagalloyl-β-D-glucose (VI), is a potent non-competitive inhibitor and shows slightly higher activity than that of kojic acid. In this study, kojic acid was used as a reference standard of tyrosinase in- hibitor due to the in vitro assay model used. Besides kojic acid, hydroquinone is known as an effective inhibitor of melanogenesis. However, hydroquinone is rarely used as a refer- ence standard in the in vitro tyrosinase inhibitory assay due to its lower tyrosinase inhibi- tory activity than that of kojic acid (2). The potent inhibitory activity on melanogenesis of hydroquinone is based on its multifunctional effects. Besides tyrosinase inhibitory activity, hydroquinone possesses many other activities in melanogenesis inhibition, such as alteration of melanosome functions, depletion of glutathione, generation of reactive Table I Inhibitory Effects of Tyrosinase Inhibitors Isolated from Root of P. suffruticosa on Mushroom Tyrosinase Activity (Substrate: L-Dopa) Sample Inhibitory activity (IC50 mM) Inhibition mode Kaempferol (I) 0.120 ± 0.006 Competitive Quercetin (II) 0.108 ± 0.009 Competitive Mudanpioside B (III) 0.368 ± 0.008 Competitive Benzoyloxypaeonifl orin (IV) 0.453 ± 0.012 Competitive Mudanpioside H (V) 0.324 ± 0.026 Competitive Pentagalloyl-β-D-glucose (VI) 0.063 ± 0.001 Noncompetitive Kojic acid 0.070 ± 0.001 Mixeda a Obtained from data in reference 18. Figure 2. Lineweaver-Burk plots of mushroom tyrosinase and L-Dopa without (♦) and with 17.5 (▲) and 35 (■) μg/ml pentagalloyl-β-D-glucose (VI).

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