CYTOSKELETON REMOVAL AND CHARACTERIZATION OF THE MICROVILLAR MEMBRANES ISOLATED FROM 2 MIDGUT REGIONS OF SPODOPTERA-FRUGIPERDA (LEPIDOPTERA)

Brush borders (microvilli) were isolated from Spodoptera frugiperda po sterior midgut cells by using the cation differential precipitation te chnique. These microvilli preparations still contained some cytoskelet on 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 cytoskel eton proteins, and causes an increase in the specific activity of the marker enzyme (aminopeptidase) and in the lipid-protein ratio of the p urified microvillar membrane, Microvilli preparations from anterior mi dgut cells seem to be free from cytoskeleton. This is supported by ele ctron 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 disas semble to permit the passage of vesicles observed migrating through th em, As a result, it is likely that the cytoskeleton is not rigid and i s lost during microvilli preparation by differential precipitation, In comparison with other insects, S, frugiperda purified microvillar mem branes have low cholesterol, carbohydrate and lipid-protein ratios, Be cause 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. (C) 1997 Elsevier Science Ltd, All rights reserved.