한국산 재래종 담배잎에서 정제한 Polyphenol Oxidase의 성상에 관한 연구

Some Properties of Polyphenol Oxidase Purified from Korean Native Tobacco Variety Leaves

Purification of polyphenol oxidase(PPO) from Korean native tobacco variety leaves was carried out through the procedure of acetone preciptation, ammonium sulfate fractionation, and Sephadex G-150 gel filtration, resulting in a 84-fold increase in specific activity. The enzyme was stable in a range of pH 7.5 to 8.0 with an optimum of pH 7.5. The optimum temperature for the enzymic reaction was about $60^{\circ}$. It was thermostable with a half-life equal to 20 min at $70^{\circ}$. Km values for (+)-catechin and pyrogallol were $1.6{\times}10^{-3}$ and $0.5{\times}10^{-3}M$, respectively. It possesses high catecholase activity but little or no cresolase activity. Lineweaver-Burk analysis of inhibition data revealed that the inhibition of (+)-catechin oxidation by potassium cyanide, 4-nitrocatechol, cystein and 2-mercaptoethanol was competitive with Ki values of $1.1{\times}10^{-6}$, $1.8{\times}10^{-6}$, $8.9{\times}10^{-6}$ and $1.3{\times}10^{-5}$, respectively.