Study on enzymatic characteristics of polyphenol oxidase in Feicheng peach fruit

Polyphenol oxidase involved in enzymatic browning was extracted from Feicheng peach fruit and its characteristics were analyzed. Results showed that the PPO activity increased 19 and 12 times respectively after adding sodium dodecyl sulfate with the substrates of 4-tert-butylcatechol and chlorogenic acid. The catalytic efficiency enhanced 11.5 and 17 times respectively. The optimum pH value increased to 6.5. And 2-hydroxy-2,4,6-tropolone was a typical competitive inhibitor. A partially denatured sodium dodecyl sulfate-polyacrylamide gel electrophoresis( SDS- PAGE) showed the presence of two active bands with apparent molecular weight of 49 ku and 50 ku. Under native isoelectric focusing(IEF),two bands existed in the acidic range with the p I of 5.7 and 5.8 both in soluble and membrane-bound tissues. A band with the isoelectric point(p I) of 5.4 was also found in membrane-bound tissues. No active band was obtained in soluble tissues of PPO. Only two kinds of antibodies were distinguished with western blotting in the three isoenzymes of membrane-bound PPO. A totally denatured SDS-PAGE and western blotting indicated the presence of a single polypeptide with a molecular weight of 60 ku.