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Journal of Applied Sciences

Year: 2013 | Volume: 13 | Issue: 6 | Page No.: 929-933
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Authors

R. Tarek Amin

E. Takwa Ellakwa

E. Doha Ellakwa

Keywords

Research Article

Properties of Phenoloxidases from the Tomato Leafminer, Tuta absoluta (Meyrick)

R. Tarek Amin, E. Takwa Ellakwa and E. Doha Ellakwa
The kinetic properties of phenoloxidases system from the fourth larval instar of the tomato leafminer, Tuta absoluta (Meyrick) were studied to detect the optimum condition for phenoloxidases-catalyzed reaction. The results of phenoloxidases activity towards catechol at different pH values revealed that the optimum pH was 5.5. The phenoloxidases activity increased gradually from 15 to 35°C and began to decline that phenoloxidases lost 60.5% of their activity at 55°C. A period of only 2 min for the tomato leafminer phenoloxidases was found to fit well within the linear part of the enzyme activity curve. On the other hand, the oxidation was directly proportional to the substrate concentration up to 10-4 M, where the peak was reached. Using Lineweaver-Burk plot, it was found that Km (Michaelis constant) was 12.98 10-6 M, while Vmax (maximum velocity of the reaction) was 0.862 O.D. units/min/mg proteins. The relatively small Km value indicates that phenoloxidases can hydrolyze catechol efficiently, even at very low concentration. The significance of results and effect of organic solvents on phenoloxidases reaction were discussed. It could be concluded that 1 mL of the reaction mixture consists of 5 μg sample protein and 0.1 mM catechol in 0.1 M phosphate buffer (pH 5.5) at 25°C for 2 min, represents the optimum condition for T. absoluta phenoloxidases system activity.
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