Isolation, partial purification and properties of polyphenol oxidase from wheat bran

Polyphenol oxidase obtained from wheat bran catalyzed the oxidation of both catechol and 4-methyl catechol. Phenolic compounds found naturally in crude extract played role as an endogeneous substrate and activity of crude extract needed correction. Activity versus enzyme concentration gave linear plot at high substrate concentration whereas nonlinear plot was obtained at low substrate concentration which proved the presence of endogeneous substrate. Phenols were tried to separate by the methods of dialysis, precipitation, ion-exchange chromatography, adsorption on celite and by treatment with PVPP. Adsorption on celite and extraction with PVPP caused the removal of phenols. Adsorption of PPO on celite yielded 4 fold increase in specific activity whereas extraction with PVPP yielded 2.5 fold increse in specific activity compared to the crude extract. The kinetics of PPO catalyzed oxidation obeyed Michaelis-Menten model, Km and V^j; values were found as 218 mM and 99 uM/min, respectively. The enzyme was inhibited by ethyl alcohol, dithiothreitol and isoproterenol and exhibited heat IVstability up to a temperature of 90 °C. The optimum pH of the enzyme was found to be 5.0. Key Words: Polyphenol oxidase, wheat bran.