PURIFICATION AND PROPERTIES OF POLYPHENOL OXIDASE FROM CABBAGE (BRASSICA-OLERACEA L)

Polyphenol oxidase (PPO) in cabbage (Brassica oleracea L.) was purified using phloroglucinol as substrate. The purified enzyme was found to be of a homogeneous state by PAGE and SDS-PAGE. The molecular weight of the enzyme was estimated to be about 39 000 and 40 000 by gel filtration and SDS-PAGE, respectively. The purified enzyme only oxidized 1,3,5-trihydroxybenzenes such as phloroglucinol (K-m = 6.4 mM) and phloroglucinolcarboxylic acid. The enzyme also had strong peroxidase (POD) activity. The optimal pH values of PPO and POD were 7.6 and 6.4, respectively, and both activities were stable in the pH ranges 6-11 at 5 degrees C for 20 h. Both activities had very high thermal stability; about 40% of the PPO and about 25% of the POD activities remained after heat treatment at 100 degrees C for 10 min. Both activities were markedly inhibited by sodium diethyldithiocarbamate and potassium cyanide. MnCl2 markedly activated PPO activity but strongly inhibited POD activity.