Produção Nacional
Digestive enzymes trapped between and associated with the double plasma membranes of Rhodnius prolixus posterior midgut cells
1988; Elsevier BV; Volume: 18; Issue: 6 Linguagem: Inglês
10.1016/0020-1790(88)90003-0
ISSN1879-2928
AutoresClélia Ferreira, Alberto F. Ribeiro, Elói S. Garcia, Walter R. Terra,
Tópico(s)Physiological and biochemical adaptations
ResumoSubcellular fractions of the cells of the posterior midgut of Rhodnius prolixus nymphs were obtained by conventional homogenization, under isotonic or hypotonic conditions, followed by differential centrifugation. Alkaline phosphatase and membrane-bound α-mannosidase are more abundant in fractions in which vesicles displaying brush-borders predominate. α-Glucosidase is associated with large membranous structures, although its subcellular distribution is different from that of alkaline phosphatase and α-mannosidase. α-Mannosidase-carrying membranes were resolved from α-glucosidase-carrying membranes in sucrose gradients, supporting the hypothesis that these enzymes are part of respectively, protein-rich inner and protein-poor outer microvillar membranes. To account for the soluble enzyme activities that sediment with vesicles displaying brush borders, major amounts of aminopeptidases are assumed to be trapped in the space between outer and inner microvillar membranes, from where they are set free by homogenization and (or) freezing and thawing. There are at least three different aminopeptidases, based on their activities toward several substrates and on sedimentation data. The results favor the view that oligomers derived from partial digestion of polymeric food are hydrolyzed down to monomers by enzymes trapped between microvillar membranes or on the surface of midgut cells. The use of microvillar membranes as a peritrophic membrane by R. prolixus is thought to be a derived character evolved from a putative phloem feeder Hemiptera ancestor.
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