CHEMICAL DETERMINATIONS IN MICROVILLAR MEMBRANES PURIFIED FROM BRUSH-BORDERS ISOLATED FROM THE LARVAL MIDGUT OF ONE COLEOPTERA AND 2 DIPTERA SPECIES

Brush-borders (microvilli) were isolated from different midgut regions of larvae of Tenebrio molitor (Coleoptera), Rhynchosciara americana ( lower Diptera), and Musca domestica (higher Diptera) by differential p recipitation from homogenates prepared as previously described. The mi crovillar preparations were treated with the chaotropic salts lithium diiodosalicylate and sodium thiocyanate in order to disrupt microvilli into microvillar membranes and core (cytoskeleton) material. Marker e nzymes were extensively inactivated and there was not a selective rele ase of cytoskeleton elements from the microvillar membranes. Insect mi crovillar preparations were also treated with hyperosmotic Tris buffer , then diluted, centrifuged, and the purified microvillar membranes we re recovered from the resulting pellet. Specific activities of marker enzymes in purified membranes were 1.5-3.0-fold higher than in the ori ginal microvillar preparations with a final yield of about 20%. Contam ination by soluble proteins was under 0.3% and by other membranes neve r exceeded 5%, as judged by chromatography in Sepharose 4B and sucrose gradient ultracentrifugation. In comparison with mammals, insect memb ranes are rich in carbohydrates (all insects studied), cholesterol (T. molitor), lipids (T. molitor), and protein (M. domestica). The densit ies, and the ratio of lipid to protein in the microvillar membranes of T. molitor is lower than that in the two species of Diptera. This agr ees with the fact that microvillar hydrolases are more important in Di ptera than in Coleoptera digestion.