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 (NP-alpha-Glu), 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-beta-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 NP-alpha-Glu and 14 mM for maltose, and hydrolyzed oligomaltodextrins up to at least maltoheptaose.