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

Polyphenol oxidase (PPO) in cabbage (Brassica oleracea L.) was purifie d using phloroglucinol as substrate. The purified enzyme was found to be of a homogeneous state by PAGE and SDS-PAGE. The molecular weight o f the enzyme was estimated to be about 39 000 and 40 000 by gel filtra tion and SDS-PAGE, respectively. The purified enzyme only oxidized 1,3 ,5-trihydroxybenzenes such as phloroglucinol (K-m = 6.4 mM) and phloro glucinolcarboxylic acid. The enzyme also had strong peroxidase (POD) a ctivity. The optimal pH values of PPO and POD were 7.6 and 6.4, respec tively, and both activities were stable in the pH ranges 6-11 at 5 deg rees C for 20 h. Both activities had very high thermal stability; abou t 40% of the PPO and about 25% of the POD activities remained after he at treatment at 100 degrees C for 10 min. Both activities were markedl y inhibited by sodium diethyldithiocarbamate and potassium cyanide. Mn Cl2 markedly activated PPO activity but strongly inhibited POD activit y.