Purification and properties of a beta-glycosidase purified from midgut cells of Spodoptera frugiperda (Lepidoptera) larvae

Two beta -glycosidases (BG) (Mr 47,000 and Mr 50,000) were purified from Sp odoptera frugiperda (Lepidoptera: Noctuidae) midguts. These two polypeptide s associate or dissociate depending on the medium ionic strength. The Mr 47 ,000 BG probably has two active sites. One of the putative active sites (ce llobiase site) hydrolyses p-nitrophenyl beta -D-glucoside (NP beta Glu) (79 % of the total activity in saturated enzyme), cellobiose, amygdalin and pro bably also cellotriose, cellotetraose and cellopentaose. The cellobiase sit e has four subsites for glucose residue binding, as can be deduced from cel lodextrin cleavage data. The enzymatic activity in this site is abolished a fter carbodiimide modification at pH 6.0. Since the inactivation is reduced in the presence of cellobiose, the results suggest the presence of a carbo xylate as a catalytic group. The other active site of Mr 37,000 BG (galacto sidase site) hydrolyses p-nitrophenyl beta -D-galactoside (NP beta Gal) bet ter than NP beta Glu, cleaves glucosylceramide and lactose and is unable to act on cellobiose, cellodextrins and amygdalin. This active site is not mo dified by carbodiimide at pH 6.0. The Mr 47,000 BG N-terminal sequence has high identity to plant beta -glyco sidases and to mammalian lactase-phlorizin hydrolase, and contains the QIEG A motif, characteristic of the family of glycosyl hydrolases. The putative physiological role of this enzyme is the digestion of glycolipids (galactos idase site) and di- and oligosaccharides (cellobiase site) derived from hem icelluloses, thus resembling mammalian lactase-phlorizin hydrolase. (C) 200 0 Elsevier Science Ltd. All rights reserved.