Biochemical characterization of digestive α-d-glucosidase and β-d-glucosidase from labial glands and midgut of wheat bug Eurygaster maura (Hemiptera: Scutelleridae)

The wheat bug Eurygaster maura (Hemiptera: Scutelleridae) is a potential pest of wheat and barley in Iran and other countries. Two major digestive enzymes of this insect, α-d-glucosidase and β-d-glucosidase, have been investigated. The midgut has four distinct regions including the first ventriculus (V1), second ventriculus (V2), third ventriculus (V3) and fourth ventriculus (V4). The study showed that the first three regions of the wheat bug midgut were acidic (pH 5.5-6), the fourth region of the midgut and hindgut pH were slightly acidic (pH 6.5-6.9) and the salivary gland (labial gland) pH was determined to be somewhat acidic (pH 5-5.5). Enzyme assay showed that α- and β-glucosidase activity is present in both midgut and salivary glands of adult E. maura. The specific activities of midgut α- and β-glucosidase were 11.2 and 10.8mU/mg protein, respectively. The specific activities of these enzymes in salivary glands were 3.06 and 2.73mU/mg protein, respectively. Optimum temperature and pH values for glucosidases were determined to be 30-35°C and 5, respectively. Glucosidases of the midgut were more stable than salivary glucosidases at 35°C. Evaluating enzymatic kinetic parameters showed that glucosidases of the midgut had more affinity as well as more velocity than that of salivary glands.