DIGESTIVE ENZYMES IN MIDGUT CELLS, ENDOPERITROPHIC AND ECTOPERITROPHIC CONTENTS, AND PERITROPHIC MEMBRANES OF SPODOPTERA-FRUGIPERDA (LEPIDOPTERA) LARVAE

In the midgut of Spodoptera frugiperda larvae, subcellular fractionati on data suggest that am in opeptidase and part of amylase, carboxypept idase A, dipeptidase, and trypsin are bound to the microvillar membran es; that major amounts of soluble dipeptidase, cellobiase, and maltase are trapped in the cell glycocalyx; and finally that soluble carboxyp eptidase, amylase, and trypsin occur in intracellular vesicles. Most l uminal acetylglucosaminidase is soluble and restricted to the ectoperi trophic contents. Aminopeptidase occurs in minor amounts bound to memb ranes both in the ectoperitrophic contents and incorporated in the per itrophic membrane. Amylase, carboxypeptidase A, and trypsin are found in minor amounts in the ectoperitrophic contents (both soluble and mem brane-bound) and in major amounts in the peritrophic membrane with con tents. Part of the activities recovered in the last mentioned contents corresponds to enzyme molecules incorporated in the peritrophic membr ane. The results suggest that initial digestion is carried out in majo r amounts by enzymes in the endoperitrophic space and, in minor amount s, by enzymes immobilized in the peritrophic membrane. Intermediate an d final digestion occur at the ectoperitrophic space or at the surface of midgut cells. The results also lend support to the hypothesis that amylase and trypsin are derived from membrane-bound forms, are releas ed in soluble form by a microapocrine mechanism, and are partly incorp orated into the peritrophic membrane. (C) 1994 Wiley-Liss, Inc.