PARTIAL-PURIFICATION AND SOME PROPERTIES OF POLYPHENOL OXIDASE EXTRACTED FROM LITCHI FRUIT PERICARP

Litchi (Litchi chinensis Sonn.) fruit peel polyphenol oxidase (PPO) wa s partially purified 21 fold by ammonium sulfate fractionation and gel filtration. Pyrogallol, catechol, and 4-methylcatechol were good subs trates for the enzyme; with no activity observed with chlorogenic acid , p-cresol, resorcinol, or tyrosine. The optimal pH for PPO activity w as 7.0 with 4-methylcatechol, with the enzyme being most stable at pH 7.4. The enzyme was relatively temperature stable with maximum activit y at 70 degrees C and requiring a little less than 10 min at 90 degree s C for 50% loss of activity. The K-m and V-max for the enzyme, with 4 -methylcatechol, were 10 mM and 1.47 x 10(4) units/min per mg protein, respectively. The enzyme was not activated by SDS. Reduced glutathion e, L-cysteine, tropolone, thiourea, FeSO4, and SnCl2 markedly inhibite d PPO activity, whereas MnSO4 and CaCl2 enhanced PPO activity. Data ob tained in this study might help to better understand and control comme rcially, litchi fruit peel browning. (C) 1997 Elsevier Science B.V.