Some biochemical properties of polyphenol oxidase from celery

Polyphenol oxidase (PPO, EC 1.14.18.1) was extracted from celery roots (Apium graveolens L.) with 0.1 M phosphate buffer, pH 7.0. The PPO was partially purified by (NH4)(2)SO4 and dialysis. Substrate specificity experiments were carried out with catechol, pyrogallol, L-DOPA, p-cresol, resorcinol, and tyrosine. The Km for pyrogallol, catechol, and L-DOPA were 4.5, 8.3, and 6.2 mM, respectively, at 25degreesC. Data for V-max/K-m values, which represent catalytic efficiency, show that pyrogallol has the highest value. The optimum pH and temperature were determined with catechol, pyrogallol, and L-DOPA. Optimum pH was 7.0 for catechol and L-DOPA, and 7.5 for pyrogallol. Optimum temperatures for maximum PPO activity were 25degreesC for pyrogallol, 40degreesC for catechol, and 45degreesC for L-DOPA. Heat inactivation studies showed a decrease in enzymatic activity at temperatures above 60degreesC. The order of inhibitor effectiveness was: L-cysteine > ascorbic acid > glycine > resorcinol > NaCl.