Heat inactivation and kinetics of polyphenoloxidase from palmito (Euterpe edulis)

Polyphenoloxidase (PPO, EC 1.14.18.1)was extracted from palmito (Euterpe edulis Mart) using 0.1 M phosphate buffer, pH 7.5. Partial purification of the enzyme was achieved by a combination of (NH₄)₂SO₄precipitation (35–90% saturation) and Sephadex G-25 and DEAE-cellulose chromatography. The purified preparation gave five protein bands on polyacrylamide gel electrophoresis, three of them with PPO activity. The K_mvalues for chlorogenic acid, caffeic acid, catechol, 4-methylcatechol and catechin were 0.57, 0.59, 1.1, 2.0 and 6.25 mM , respectively. PPO has a molecular weight of 51 000 Da, maximum activity at pH 5.6 with chlorogenic acid as substrate, and was stable between pH 5.0 and 8.0. The enzyme was heat stable at 50–60°C and inactivated at 75°C. The heat stability of palmito PPO was found to be pH dependent; at 50°C and pH 4.0 the enzyme was fully inactivated after 30 min. The pH/activity studies showed two groups with pK values c 4.6 and 6.7 involved in PPO catalysis.