›› 2004, Vol. 47 ›› Issue (3): 305-309.doi:

• RESEARCH PAPERS • Previous Articles     Next Articles

Comparison on properties of polyphenoloxidase from Pieris rapae (L.) in different stages and instars

XUE Chao-Bin1, CHEN Qing-Xi2, WANG Qin2, KE Li-Na2, LUO Wan-Chun1*   

  • Online:2004-06-20 Published:2004-06-20
  • Contact: LUO Wan-Chun

Abstract: The kinetic properties of polyphenoloxidase (PPO) from Pieris rapae (L.) in different stages and instars were studied and compared. The results showed that the polyphenoloxidase activity was different at different stages and instars in this insect. The enzyme activity of the 5th instar was the highest and that of the pupa was the lowest. The order of the enzyme activity was the 5th instar > prepupa > the 4th instar > the 3rd instar > pupa. The effect of pH on the activity of polyphenoloxidase was studied, and the results showed that the optimum pH was the same value in all of the stages and instars and the best pH value for the oxidation of catechol was 7.0±0.2. The optimum temperature of the polyphenoloxidase activity was very variable in the tested stages and instars of the insect. The optimum temperature for the 3rd instar, 4th instar, 5th instar, prepupa and pupa was 36.0±0.5℃, 38.±1.0℃, 43.0±1.0℃, 45.5±1.0℃ and 50.0±1.5℃, respectively, indicating that the optimum temperature of the pupa was the highest. The activation energy of the enzyme from this insect for the oxidation of catechol was 43.10±0.28, 36.50±0.27, 5.79±0.32, 30.10±0.21 and 58.88±0.39 kJ/mol for the 3rd instar, 4th instar, 5th instar, prepupa and pupa, respectively. The kinetic parameters for the oxidation of catechol and L-DOPA by polyphenoloxidase from the different stages and instars were determined and compared.

Key words: Pieris rapae; polyphenoloxidase, enzyme activity, kinetic properties