关键词:  南亚果实蝇, 发育阶段, 多酚氧化酶, 酶活性, 动力学特性

Abstract:  【Objective】 This study aims to determine the activities of polyphenoloxidase (PPO) in the fruit fly Bactrocera tau (Walker) during various developmental stages. 【Methods】 The PPO activity and kinetic properties in the 1st, 2nd and 3rd instar larva, pupa and adult were determined with spectrophotomethrical method using catechol as the substrate. 【Results】 The PPO activities varied significantly during different developmental stages of B. tau. The enzyme activity in  the 3rd instar larva was the highest (434.42 U/mg) and that in pupa was the lowest (231.05 U/mg). At pH 6.5, the enzyme activities in the 1st, 2nd and 3rd  instar larva, pupa and adult were 265.42，  358.34, 444.42，  210.02 and 373.99 U/mg, respectively. However, PPO activities decreased dramatically at pH levels above 7.0 or below 5.0. At 34℃ and 37℃, PPO activities stayed at a high level, while the enzyme activities significantly decreased at above 40℃ or below 27℃. When catechol was used as the substrate, the measured Michaelis-Menten constant (K_m) and maximum velocity (V_max) of PPO in 2nd instar larva were 3.10 mmol/min and 476.19 mmol/L, respectively; but those in pupa were 0.63 mmol/min and 50.25mmol/L, respectively, indicating that the catalytic activity of PPO in 2nd instar larva to the substrate catechol was higher than that in pupa. When L-DOPA was used as the substrate, the measured K_m and V_max of PPO in the 3rd instar larva were 0.49 mmol/min and 188.68 mmol/L, respectively; in contrast, the K_m (0.25 mmol/min) and V_max (21.79 mmol/L) of PPO in pupa were relatively lower. 【Conclusion】 Our results indicate that the properties of PPO in B. tau at different temperature and pH values are closely associated with its developmental stage.

Key words: Bactrocera tau, developmental stage, polyphenol oxidase, enzyme activity, kinetic property