Purification and Characterization of a Polyphenol Oxidase from the Kew Cultivar of Indian Pineapple Fruit

Abstract

Three isoforms of polyphenol oxidase (PPO) were purified to apparent homogeneity from the Kew cultivar of Indian pineapple fruit in a four-step procedure. The major isoenzyme, with a yield of 45%, was found to be a tetramer of identical subunits of molecular mass ≈25 kDa. An ionic strength dependent association−dissociation equilibrium was observed with pineapple PPO. Amino acid analysis of the major isoenzyme indicated the presence of a high content of glutamic acid, glycine, and serine and a low content of the sulfur-containing amino acids. The enzyme was optimally active between pH 6 and 7. The PPO did not show any cresolase activity, and the preferred substrates were diphenols. Ascorbic acid, l-cysteine, and potassium metabisulfite were found to be potent inhibitors of PPO. Keywords: Catecholase; pineapple fruit; polyphenol oxidase; PPO-isoenzyme; association−dissociation