Cytoskeleton removal and characterization of the microvillar membranes isolated from two midgut regions of Spodoptera frugiperda (Lepidoptera)

Abstract

Brush borders (microvilli) were isolated from Spodoptera frugiperda posterior midgut cells by using the cation differential precipitation technique. These microvilli preparations still contained some cytoskeleton elements visible by electron microscope. These elements are removed by Tris treatment followed by dilution and ultracentrifugation. Tris treatment solubilizes protein with M r values similar to some cytoskeleton proteins, and causes an increase in the specific activity of the marker enzyme (aminopeptidase) and in the lipid–protein ratio of the purified microvillar membrane. Microvilli preparations from anterior midgut cells seem to be free from cytoskeleton. This is supported by electron microscopy and by the absence, after Tris treatment, of changes in the specific activity of the marker enzyme and in the lipid–protein ratio. The cytoskeleton of these microvilli should assemble and disassemble to permit the passage of vesicles observed migrating through them. As a result, it is likely that the cytoskeleton is not rigid and is lost during microvilli preparation by differential precipitation. In comparison with other insects, S. frugiperda purified microvillar membranes have low cholesterol, carbohydrate and lipid–protein ratios. Because S. frugiperda midgut microvillar membranes almost lack intrinsic digestive enzymes, their low lipid–protein ratios might result from a large amount of carrier or other proteins.