Properties of glycosidases from the maize weevil, Sitophilus zeamais

A survey of glycosidase activity in adults of the maize weevil, Sitophilus zeamais Motschulsky, indicated a complex of enzymes qualitatively sufficient to hydrolyze the free di- and oligosaccharides in their cereal diets as well as the maltose and oligomaltodextrins produced by the action of α-amylase on ingested starch. Glycosidase activity was found primarily in the soluble fraction (105,000 g supernatant) of gut (foregut, midgut and contents) homogenates and was most active in buffers with slightly acidic pH. α-Glucosidase activity was detected by using $\text{p-}\text{nitrophenyl}\text{-α-}\text{d}\text{-glucopyranoside}$ (NPαGlu), maltose, sucrose and melezitose as substrates. Based on differences in pH optima, there may be a specific α-trehalase. β-Glucosidase activity was detected with $\text{p-}\text{nitrophenyl}\text{-β-}\text{d}\text{-glucopyranoside}$ and cellobiose. $\text{p-}\text{Nitrophenyl}\text{-α-}\text{d}\text{-galactopyranoside}$ was not hydrolyzed but the slow hydrolysis of melibiose indicated the presence of an α-galactosidase. β-Galactosidase was detected with $\text{p-}\text{nitrophenyl}\text{-β-}\text{d}\text{-galactopyranoside}$. Raffinose was slowly hydrolyzed. The molecular mass of α-glucosidase, partially purified from adult weevils by ammonium sulfate precipitation and ion exchange chromatography, was estimated to be 130 kDa under non-dissociating conditions. α-Glucosidase activity was detected at R_m 0.43 on 7.5% acrylamide gels with 4-methyl-umbelliferyl-α-d-glucoside as substrate. pI was estimated to be 4.9 by isoelectric focusing. Two fractions with activity against $\text{p-}\text{nitrophenyl}\text{-α-}\text{d}\text{-glucopyranoside}$ were resolved by high performance liquid chromatography. One fraction (peak No. 2) was highly specific for maltose, had K_m values of 12.9 mM for NPαGlu and 14 mM for maltose, and hydrolyzed oligomaltodextrins up to at least maltoheptaose