LAUSR

Abstract Catalase (CAT) is an anti-oxidative enzyme and plays a crucial role in protecting insects against harmful reactive oxygen species (ROS).In this study, we estimated CAT in different major organs including whole gut, cuticle, fat body, head and haemolymph of the 10th instar larvae of Rhynchophorus ferrugineus, the major pest of all palm varieties in the world. Among the examined organs, the fat body displayed the highest CAT activity. The CAT activity in fat body was tracked during larval development and ranged from 420 ± 10 to 8000 ± 70 U/insect with specific activities ranged from 280 to 1942 U/mg protein. A monofunctional R. ferrugineus CAT isoenzyme was purified to homogeneity from the 12th instar larva that recorded the highest enzyme level. The enzyme exists in homotetrameric form with subunit molecular weight of 44kDa and specific activity of 8652.5 U/mg proteins. It showed optimum activity at pH 7.5 and was thermally stable up to 40 °C. R. ferrugineus CAT was inhibited by most of the cations examined. Furthermore, sodium azide and salicylic acid were potent inhibitors to CAT enzyme with IC50 of 0.1 and 0.5, respectively. It had Km and Vmax values for H2O2 of 20 mM and 227 U/min/ml, respectively. The comparison between the characteristics of R. ferrugineus CAT and those of other insect species seemed to be useful for developing the strategies of R. ferrugineus control.