Abstract: The kinetic properties of polyphenol oxidase (PPO) from Semiothisa cinerearia Bremer et Grey, a forestry insect, were studied after the enzyme was partially purified by 40% saturated (NH₄)₂SO₄ and Sephadex G-100 gel filtration. The results showed that the 6.96fold purification was achieved from the crude enzyme. The affinities of PPO with the substrates pyrogallol, catechol and Ldopamine (LDOPA) were not different significantly, and the K_m with the three substrates was 0.23 mmol/L, 0.48 mmol/L and 0.49 mmol/L, respectively. The optimum pH was 7.0 and the best temperature was 37℃ for the tested PPO. The effects of two compounds as inhibitors of the reaction catalyzed by the enzyme were also tested. Those results indicated that quercetin could inhibit the PPO activity through competitive inhibition and thiourea could also inhibit the enzyme activity but through noncompetitive reaction.

Key words: Semiothisa cinerearia; polyphenol oxidase, purification, inhibitor, kinetic properties