Polyphenol oxidase from Mazruma grape (Vitis vinifera L.)

Polyphenol oxidase of Mazruma grape (Vitis vinifera L. Mazruma) which is one of the most widely grown grape species in the south-eastern Anatolia region of Turkey was extracted and partially purified through ammonium sulphate precipitation and dialysis. The sample was used for characterization of the polyphenol oxidase. The enzyme showed affinity towards dihydroxy phenolic substrates but no activity towards monohydroxy phenols. The best substrate of the PPO was found to be 4-methylcatechol (highest V-max value). Optimum pH and temperature were found to be pH 6.5 and 20 degreesC, and K-M and V-max values were 6.8 mM and 2560 EU/mLmin with 4-methylcatechol, respectively. Inhibition studies indicated that L cysteine, sodium cyanide, ascorbic acid and sodium diethyl dithiocarbamate were the most effective, being able to completely inhibit enzyme activity at 5.0 mM concentration. Heat inactivation studies showed that temperature > 40 degreesC resulted in loss of enzyme activity, The enzyme was inactivited 77%, 86% and 94% after heating for 60 minute at temperatures of 50 degreesC, 60 degreesC and 70 degreesC respectively, and was competely inactivited at 80 degreesC after 10 min.