#alpha#-Galactosidases from the larval midgut of Tenebrio molitor (Coleoptera) and Spodoptera frugiperda (Lepidoptera)

摘要

There are three midgut a-galactosidases (To1, To2, To3) from Tenebrio molitor larvae that are partially resolved by ion-exchange chromatography. The enzymes have approximately the same pH optimum (5.0), pI value (4.6) and Mr value (46000-49000) as determined by gel filtration or native electrophoresis run in polyacrylamide gels with differen1 concentrations. Substrate specificities and functions were proposed for the major T. molitor midgut a-galactosidase! (To2 and To3) based on chromatographic, carbodiimide inactivation, Tris inhibition, and on substrate competitior data. Thus, To2 would hydrolyse a-1,6-galactosaccharides, exemplified by raffinose, whereas To3 would act or melibiose and apparently also on digalactosyldiglyceride, the most important com~und in the thylacoid membranes oj chloroplasts. Most galactoside digestion should occur in the lumen of the first two thirds of T. molitor larval midguts since a -galactosidase activity predominates there. Spodoptera frugiperda larvae have three midgut a -galactosidases (SO 1. So2, So3) partially resolved by ion-exchange chromatography. The enzymes have similar pH optimum (5.8), pI value (7.2) and Mr value (46000-52000), and at least the major a-galactosidase must have an active carboxyl group in the active site. Based on data similar to those described for T. molitor, SOl and So3 should hydrolyse melibiose and So~ should digest raffinose and, perhaps, also digalactosyldiglyceride. The midgut distribution of a-galactosidase activity supports the proposal that a-galactosidase digestion occurs at the surface of anterior midgut cells in SpodopterG frugiperda larvae.