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 alpha-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. alpha-Glucosidase activity was detected by using p-nitrophenyl-alpha-D-glucopyranoside (NPalphaGlu), maltose, sucrose and melezitose as substrates. Based on differences in pH optima, there may be a specific alpha-trehalase. beta-Glucosidase activity was detected with p-nitrophenyl-alpha-D-glucopyranoside and cellobiose. p-Nitrophenyl-alpha-D-galactopyranoside was not hydrolyzed but the slow hydrolysis of melibiose indicated the presence of an alpha-galactosidase. beta-Galactosidase was detected with p-nitrophenyl-beta-D-galactopyranoside. Raffinose was slowly hydrolyzed. The molecular mass of alpha-glucosidase, partially purified from adult weevils by ammonium sulfate precipitation and ion exchange chromatography, was estimated to be 130 kDa under non-dissociating conditions. alpha-Glucosidase activity was detected at R(m) 0.43 on 7.5% acrylamide gels with 4-methyl-umbelliferyl-alpha-D-glucoside as substrate. pI was estimated to be 4.9 by isoelectric focusing. Two fractions with activity against p-nitrophenyl-alpha-D-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 NPalphaGlu and 14 mM for maltose, and hydrolyzed oligomaltodextrins up to at least maltoheptaose.