Purification and characterization of dog-rose (Rosa dumalis Rechst) polyphenol oxidase

Polyphenol oxidase (PPO) of dog-rose fruit was extracted and purified through (NH4)(2)SO4 precipitation, dialysis, gel filtration, and DEAE-Sephacel ion-exchange chromatography. The sample obtained from ammonium sulfate precipitation and dialysis was used for characterization of the PPO. For this aim, optimum conditions, i.e., pH, temperature, and ionic strength, were determined with eight substrates. The best substrate of the PPO was found to be 4-methylcatechol. Optimum pH and temperature were found at pH 8.5 and 20 degrees C, and K-M and V-max values were 8.64 mM and 431.96 with 4-methylcatechol, respectively. Eleven inhibitors were tested in the study and the most effective was found to be sodium metabisulfide as competitive inhibitor. The PPO has showed renaturation property after it denatured, as well. Therefore, heat inactivation process for preventing enzymatic browning of dog-rose fruit products is not recommendable. Two isoenzymes of the PPO were detected by polyacrylamide slab gel electrophoresis.