Enzyme property of polyphenol oxidase isoenzyme from sweet potato

• 1、School of Life Science, South China Normal University, Guangzhou, 510631

Abstract：Polyphenol oxidase (PPO) is a multi-copper enzyme, which widely distributes in the biosphere, and is used in various industrial aspects, such as fresh product browning control and organic synthesis. There is rather high PPO activity in sweet potato, and it is of great significance for the further application and development to investigate the enzymatic property. However, the current research on the PPO enzymatic property of sweet potato mainly focuses on the PPO enzyme extracts containing multiple isozymes rather than the single PPO isozyme. Therefore, the investigation on enzyme activity of the PPO isozyme in sweet potato is carried out in this study, in order to build the foundation for its deep research on the mechanism of catalytic reaction. Three kinds of isozymes of PPO were separated from white sweet potato by adopting several methods, including isoelectric precipitation, organic reagents precipitation, Sephadex G-75 gel filtration chromatography and electrophoretic method for elution. The part enzymatic properties of isozyme were studied with catechol as the substrate. And then the enzyme kinetic parameters were determined under the optimum condition for the enzymatic reaction. The result showed that the optimal pH values were all 6 for the enzymatic reaction of PPO I, PPO II and PPO III, while the optimal temperature were25 C, 30 C and 30 C, respectively. When the concentrations of substrate reached0.06 mol/L, 0.05 mol/L and 0.06 mol/L respectively for PPO I, PPO II and PPO III, the enzymatic activity reached the peak and become stable. The low concentration of Cu2+ played positive role in promoting the enzymatic activity. With catechol as the substrate, the Km values of the PPO I, PPO II and PPO III were 0.013 mol/L, 0.018 mol/L and 0.022 mol/L, and their affinity degree to catechol reduced in order.

Keywords： Food biochemistry white sweet potato polyphenol oxidase isozyme enzymatic property