Studies on the Effect of Graptopetalum paraguayense extract on the Mushroom Tyrosinase Activity

• Main Authors: Yi-Wei Chen, 陳奕瑋
• Other Authors: Keh-Feng Huang
• Format: Others
• Language: en_US
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/z76wmr

碩士 === 靜宜大學 === 應用化學系 === 90 === Tyrosinase or polyphenol oxidase (EC1.14.18.1) is a copper-containing enzyme that is widespread in nature. It is responsible for not only melanization in animals but also browning in plants. In recent years, there is an increasing interest in finding natural tyrosinase inhibitors from plants and microorganisms. The tyrosinase inhibitors should have broad applications, especially in medicinal and cosmetics products in relation to hyperpigmentation. This study was aimed to evaluate the tyrosinase inhibitory activity of water or 50% ethanolic extracts from Graptopetalum paraguayense. The results were also compared with those obtained from the well-known tyrosinase inhibitors, benzoic acid and kojic acid. The results showed that the water or 50% ethanolic extracts of Graptopetalum paraguayense had tyrosinase inhibitory activity on the L-Dopa oxidation by mushroom tyrosinase. It was also found that the inhibitory activity increased with the concentrations of extracts to a certain extent and then leveled off as the concentration further increased. The 50% ethanolic extracts of Graptopetalum paraguayense had higher tyrosinase inhibitory activity than the water extracts, as evidenced by the lower half-inhibition concentration (IC50) needed for this oxidation. As compared to the well-known tyrosinase inhibitors, the Graptopetalum paraguayense extracts showed less inhibitory activity than benzoic acid and kojic acid. The inhibition was also a function of pH, becoming less as the pH was increased. In addition, the inhibition kinetics analyzed by a Dixon plots found that the Graptopetalum paraguayense extract to be a competitive inhibitor for this oxidation. The results of this study implied that Graptopetalum paraguayense had tyrosinase inhibitory activity.