Purification and properties of polyphenol oxidase from leaf lettuce (Lactuca sativa)

概要

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The polyphenol oxidase (<I>o</I>-diphenol : oxygen oxidoreductase, EC. 1.10.3.1, PPO) of leaf lettuce was purified about 23.4-fold with a recovery rate of 13.3% by ammonium sulfate fractionation, ion exchange chromatography, hydrophobic chromatography, and gel filtration. The purified enzyme appeared as a single band on polyacrylamide gel electrophoresis (PAGE) and SDS-polyacrylamide gel electrophoresis (SDS-PAGE). The estimated molecular weights of the enzyme were about 45, 000 and 46, 000 as determined by gel filtration and SDS-PAGE, respectively. The purified enzyme strongly oxidized chlorogenic acid and (-) -epicatechin. The Km (Michaelis constant) values of the enzyme were 1.0 mM for chlorogenic acid (pH 5.0, 30°C) and 1.4 mM for (-) -epicatechin (pH 8.0, 30°C). The optimum pHs of the enzyme were 5.0 for chlorogenic acid oxidase (ChO) and 8.0 for (-) -epicatechin oxidase (EpO). In the pH range from 5 to 8, both activities of ChO and EpO were stable at 4°C for 22h. The optimum temperatures of both activities were 30°C. Both activities were stable up to 50°C after heat treatment for 10 min. The purified enzyme was strongly inhibited by L-ascorbic acid and L-cysteine at 5 mM. These results suggest that the enzymatic browning of leaf lettuce is prevented by treatment with sodium chloride, L-ascorbic acid or L-cysteine at 5 mM.
日本食品保蔵科学会の論文