Gut PH, and Isolation and Characterization of Digestive α-D-Glucosidase of Sunn Pest

A study of insect digestive enzymes makes sense given that the gut is the major interface between the insect and its environment. An understanding of gut and digestive enzyme function is essential when advanced methods of insect management such as application of enzyme inhibitors and transgenic plants are developed to control insect pests. The aim of the current research project was to study midgut anatomy, midgut pH and α-glucosidase activity in Sunn pest, Eurygaster integriceps Puton (Hemip: Scutelleridae). Sunn pest midgut is comprised of four distinct regions including first ventriculus (V1), second ventriculus (V2), third ventriculus (V3) and finally fourth ventriculus (V4). The study showed that the first three regions of the Sunn pest midgut are more acidic (pH= 5–5.2), the fourth region moderately acidic (pH= 6.2–6.4), and hindgut slightly acidic (pH= 6.5–6.8). Enzyme assay showed that α-glucosidase activity is present in midgut and salivary glands of adult E. intergriceps. The specific activity of midgut enzyme was 0.17 U mg protein-1 while the specific activity of the salivary glands enzyme was 0.033 U mg protein-1. Optimum temperature and pH values for α-glucosidase were determined to be 40-45°C and 5, respectively. Based on linear regression analysis of reciprocal p-nitrophenyl substrate (p-nitrophenyl α-D-glucopyranoside) concentration versus reciprocal α-glucosidase activity Km and Vmax were 17 and 0.9 mM p-nitrophenol min-1, respectively. The effect of different ion concentrations on α-glucosidase activity showed that Na+, K+, Mg2+, and Ca2+ ions exerted positive effects on the enzyme activity. Other compounds tested such as urea, SDS, Tween 80, Triton X-100 and EDTA had an inhibitory effect on enzyme activity.