THE PARTIAL PURIFICATION AND PROPERTIES OF POLYPHENOL OXIDASE FROM THE PERICARP OF LITCHI (LITCHI CHINENSIS)
Tan Xing-jie and Li Yue-biao(South China Institute of Botany, Academia Sinica)
Polyphenol oxidase (o-diphenol: oxygen oxidoreductase, EC1. 10. 3. 1) which causes browning of Litchi pericarp after harvest was partially purified with an 8.2-fold increase of specific activity by acetone precipitation followed by ammonium sulfate fractionation. The enzyme could use some polyphenols as substrate, but did not oxidize monophenols. It was stable, no activity change occurred within one hour at a temperature below 40℃, while the activity decreased rapidly above 55℃. The optimal reaction temperature was 35℃. With pyrogallol, D,L-3,4-dihydroxyphenylalanine or catechol as substrate, the Km was 1.85, 2.5 or 5.0 mM and Vmax was 41.62×10~3,0.85×10~3 or 0.24×10~3 units min~(-1) mg~(-1) protein, respectively. The enzyme was strongly inhibited by sodium bisulfite and sodium diethyldithiocarbamate, the latter appeared to inhibit the enzyme non-competitively, with a Ki of 0.05 mM.