Study on enzymatic properties of 67.8ku polyphenol oxidase in loofah

Objective:To study the enzymatic properties of 67.8ku PPO in loofah. Methods:Polyphenol oxidase of 67.8ku was extracted and purified from loofah and the effect of tempere, pH, substrats, metal ions, inhibitors and surfactants on PPO activity were researched respectively. Results:The enzyme activity was the strongest when pH value was 6.0 and its activity was stable in pH3.0⁸.0. The optimum temperature of PPO was 30℃ and its thermostability was good. After 120min of keeping 70℃, its relative activity was 40%. The enzyme was activated by Co2+, K+and Ca2+, but inhibited by Na+, Mg2+and Cu2+. Ascorbic acid was the best inhibitor of the PPO, followed by cysteine, β-Mercaptoethanol, sodium thiosulfate and sodium sulfite. Some surfactants had significant stimulation to the enzyme activity such as Laurouyl Sarcosine and SDS, but some had inhibiton such as CTAB and Tween-20. The binding ability of l-dopa with the enzyme was the strongest, taking it as substrate, the value of Km and Vmax of PPO were 1.32mmol/L and 0.22OD475 /min respectively. Conclusion:The study identified the optimum conditions and the critical factors affected its activity of PPO in loofah, it could provide theoretical basis for the prevention of enzymatic browning during storage and processing of the loofah.