Abstract: By in vitro enzymatic reaction,the kinetic parameters and mechanism of Gypenosides on tyrosinase were compared with their selenium-complexes.L-tyrosine and L-DOPA were used as substrates to simulate the catalytic oxidation process of tyrosinase monophenol and diphenol enzyme in vitro.The Ki valures of gypenoside on 50%,70% ethanol elution segments and gypenoside-selenium complexes on 50%,70% ethanol eluting gypenoside on tyrosinase were 1.533,1.767,1.312,and 1.210 mmol/L respectively.The lower Ki value indicated that higher concentrations of Selenium could enhance higher inhibitory effect of Gynostemma pentaphyllum on tyrosinase,otherwise,the oxidation stage of monophenolase was a quick step.The kinetic analysis of enzyme reaction showed that the inhibitory effects of four gypenosides and its selenium-complexes on tyrosine were all mixed-competitive inhibition.The specific pharmacological and chemical characteristics provided a theoretical basis and reference for further research and development of Gynostemma pentaphyllum and selenium related whitening cosmetics.

Key words: Gypenoside-selenium complex, tyrosinse, inhibition