Polyphenol oxidase (PPO) was extracted from Sultaniye grapes grown in Turkey, and its characteristics in terms of pH and temperature optima, thermal inactivation, kinetic parameters and potency of some PPO inhibitors were studied. Optimum pH and temperature for grape PPO were found to be 3.4 and 30 degrees C, using catechol as substrate. K. and V-max values were found to be 44.5 +/- 5.47 mm and 0.695 +/- 0.0353 OD410 min(-1) respectively. Four inhibitors were tested in this study and the most potent inhibitor was sodium metabisulphite, followed by ascorbic acid. From the thermal inactivation studies in the range of 6580 degrees C, the half-life values of the enzyme ranged between 2.6 and 49.5 min. Activation energy (Ea) and Z values were calculated to be 208.5 kJ mol(-1) r(2) = 0.9544) and 10.95 degrees C (r(2) = 0.9517), respectively.