Polyphenol oxidase (PPO) of Malatya apricot was isolated by (NH4)2SO4 precipitation and dialysis. PPO showed activity to catechol, l-dopa, and gallic acid. Catechol was the most suitable substrate for Malatya apricot PPO (lowest K m value). The optimum pH for the PPO was 8.5. Heating for 40 min at 40 °C did not cause a significant loss of enzymic activity. The times required for 50% inactivation of activitiy at 60 and 80 °C were found to be 47 and 16 min, respectively. The I 50 values of inhibitors studied on PPO were determined by means of activity percentage [I] diagrams. The values were 2.7 × 10-5, 5.03 × 10-5, 3.62 × 10-5, 3.68 × 10-5, and 8.30 × 10-4 M for sodium metabisulfite, ascorbic acid, 2-mercaptoethanol, thiourea, and salicylic acid, respectively. Ascorbic acid, 2-mercaptoethanol, sodium metabisulfite, and thiourea inhibited the reaction strongly. Keywords: Malatya apricot; Prunus armeniaca L.; polyphenol oxidase; inhibitors

Polyphenol oxidase (PPO) was isolated from Allium sp. PPO showed activity to catechol and dl-dopa (K m values were 25 mM for cathecol and 33 mM for dl-dopa;V max values were 666 EU/mL·min for cathecol and 166 EU/mL·min for dl-dopa). Catechol was the most suitable substrate for Allium sp. PPO (lowest K m value). The optimum pH for the PPO was 7.5 on substrates catechol and dl-dopa. Heat inactivation studies showed temperature >40 °C resulted in loss of enzyme activity. Heating for 30 min at 40 °C did not cause a significant loss of enzymatic activity. Allium sp. PPO was significantly inhibited in the presence of ascorbic acid, 2-mercaptoethanol, and sodium metabisulfide. Keywords: Polyphenol oxidase; Allium sp.; inhibitors; herb cheese