Characterization of purified Polyphenol oxidase (PPO) from (Lactuca serriola L.) Prickly lettuce


n this study, purified PPO from Prickly lettuce were obratind from a previous characterization study. The results showed that the optimum pH were 6.5 and the pH stability profile showed that the enzyme were more stable at pH values 5.5-8, the optimum temperature for enzyme activity were 35ºC and the enzyme were stable at 35ºC for 10 min. the activation energy for conversion of substrate to product was 39.7194 Kj/mol, the purified enzyme lost its activity after 5 days of storage at 25ºC, while it lost (73 , 16)% of primary activity after 21 days of storage at 4 and -18ºC respectively, the purified enzyme contains 7.2% carbohydrates. It was noticed that all treated of enzyme with L-Cystein, Sodium metabisulphate and Dithiothretol at 1 and 10 mM revealed high inhibition for the enzyme activity, followed by citric acid, L-Ascorbic acid, EDTA and Potassium cyanide, while both Thiourea and Sodium benzoate showed less inhibitory effect. The Km and Vmax were (4.762 , 0.0588) mM/min respectively, while the coefficient Vmax/Km were 0.01235 min-1 for the purified enzyme when used Catechol as a substrate.