Characterization of Phenoloxidase in The Red Palm Weevil; Rhynchophorus ferrugineus (Olivier) (Coleoptera: Curculionidae) (Olivier) Using Catechol Substrate

Document Type : Original Article

Authors

1 Department of Pest Physiology, Plant Protection Research Institute (PPRI), Agricultural Research Center (ARC), Dokki, Giza, Egypt.

2 -Department of Pest Physiology, Plant Protection Research Institute (PPRI), Agricultural Research Center (ARC), Dokki, Giza, Egypt -Department of Biology, University Collage of Taymaa, University of Tabouk (ut), Kingdom of Saudi Areabia(Ksa)

Abstract

Phenoloxidases (EC.1.14.18.1) are implicated in the immunity of insects toward microorganisms, so oxidative enzymes such as phenoloxidases (PO) from the 7th instar larvae of the red palm weevil; Rhynchophorus ferrugineus (Oliv.) was partially isolated to characterize its activity using catechol as a substrate. The mitochondrial fraction of larval homogenate was used as enzyme source for partial kinetic studies.Enzyme catalysis was directly proportional to enzyme crude protein conc. up to 200 ug contained in 1 ml of the reaction mixture. Michaelis-Menten kinetics of PO activity was evaluated by constructing Lineweaver Burk double reciprocal plot. Michaelis constant (Km) was, 3.45 X10-4 M and maximum velocity (V max) of PO reaction was 344.8 O.D.min-1 mg protein-1. Effect of pH, temperature and substrate concentration on enzyme reaction was tested. Generally, each variable was chosen while other conditions were at optimum found primarily. Reaction rate was optimal at 10-1 N catechol, neutral medium (pH 7) and 40 C. PO kept its most activity when incubated at 60 C for 15 min before reaction initiation. Phenoloxidases efficiently catalyze catechol. Results in the present study may probably offer a fundamental anchor for future alternative strategies in controlling R. ferrugineus via obstructing its innate defence mechanisms.

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