Polyphenol oxidase (PPO) was extracted and purified from Turkish Alyanak apricot variety and its characteristics were studied in two consecutive years (2008 and 2009). Three isoenzymes (isoenzyme A1, A2 and B) were obtained upon ammonium sulfate fractionation, ion exchange chromatography using DEAE-Toyopearl 650 M and gel filtration chromatography using Sephadex G-100. The isoenzymes exhibited different kinetic properties. Furthermore, year-to-year variability in K-m and V-max values was significant. The pH optimum for enzyme activity was 4.98 for isoenzymes A1 and A2, and 5.8 for isoenzyme B. The isoenzymes A1 and B had optimum temperature at 30 degrees C in both years whereas isoenzyme A2 had maximum activity at 40 degrees C in 2008 and 30 degrees C in 2009. The inactivation kinetics parameters and the effects of inhibitors tested exhibited significant year-to-year variation. (C) 2015 Elsevier Ltd. All rights reserved.