Polyphenol oxidase (PPO) of Malatya apricot was isolated by (NH4)(2)SO4 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 degrees C did not cause a significant loss of enzymic activity. The times required for 50% inactivation of activitiy at 60 and 80 degrees 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 x 10(-5), 5.03 x 10(-5), 3.62 x 10(-5), 3.68 x 10(-5), and 8.30 x 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.