Polyphenol oxidase (PPO) was extracted from Emir 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. The optimum pH and temperature for grape PPO were found to be 4.2 and 25 degrees C respectively using catechol as substrate. K-max and V-max values were found to be 25.1 +/- 2.72 mmol L-1 and 0.925 +/- 0.04 OD410 min(-1) respectively. Of the inhibitors tested, the most potent was sodium metabisulfite, followed by ascorbic acid. The thermal inactivation curve was biphasic. Activation energy (E-a) and Z values were calculated as 251.4 kJ mol(-1) (r(2) = 0.996) and 8.92 degrees C (r(2) = 0.993) respectively. @ 2006 Society of Chemical Industry.