Characterization of Polyphenoloxidase from Stanley Plums.

Five plum cultivars were investigated for polyphenoloxidase. Stanley cultivar, which showed highest PPO activity, was selected for characterization of this enzyme. The activity of crude enzyme was 3.5 times greater in the flesh than in the skin of the fruit. The enzyme showed a Km of 20 mM of catechol and Vmax of 5.41 x 10−1 O.D./min at pH 6.0. Its pH and temperature optima were 6.0 and 20°C respectively. The enzyme lost activity below pH 4.5, but was stable even at 70°C. Among substrates, 4-methylcatechol was oxidized more rapidly, although catechol, dopamine, pyrogallol and caffeic acid were also good substrates. The enzyme was strongly inhibited by sodium metabisulfite Na2S2O5), L-cysteine and ascorbic acid. [ABSTRACT FROM AUTHOR]