Characterization of polyphenoloxidase (PPO) extracted from 'Jonagored' apple

Polyphenoloxidase (PPO) was extracted from apple (cv. Jonagored) with addit ion of 2% PVP and 0.25% Triton X100 to the extraction buffer containing phe nolic adsorbents. Experiments were performed to evaluate the affinity and s pecificity towards several substrates. 'Jonagored' apple PPO was found to h ave higher specificity (lower K-m) towards L-dopa, 4-methylcatechol and (+) catechin than other phenols tested, but the highest activity level was obt ained with p-cresol. The ratio V-max/K-m indicates that p-cresol followed b y L-dopa and 4-methylcatechol are the best substrates for 'Jonagored' apple PPO. The enzyme activity showed two pH optima, at 5.0 and 7.5, at room tem perature, with the main peak at pH 7.5 and the secondary one at pH 5.0 when catechol was the substrate. (C) 2000 Elsevier Science Ltd. All rights rese rved.