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Enzymology of Plasma Membranes of Insect Intestinal Cells 总被引:2,自引:0,他引:2
The enzymology of insect intestinal cell plasma membranes isa field of scientific research that is in the earliest stagesof development. In this paper the few published studies specificallydesigned to isolate plasma membranes from insect intestinalcells and determine the enzymes associated with them are reviewedin light of both older studies that approached these problemsless directly and recent results from our laboratory. In the past few years reliable methods have been developed forthe isolation of specific portions of plasma membranes fromthe epithelial cells of the midguts of a few insect larvae.These membrane preparations have been assayed for a varietyof enzyme activities. Alkaline phosphatase, leucine aminopeptidaseand -glutamyl transpeptidase have shown promise as potentialmarkers for the plasma membranes of insect larval midgut cells.However, only the latter enzyme currently stands unchallengedas a marker for the apical portion of the plasma membrane ofinsect midgut columnar epithelial cells. No enzymes can yetbe considered to be even tentatively established as markersfor the basal or lateral portions of insect intestinal cells. 相似文献
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HARVEY WILLIAM R.; CIOFFI MOIRA; WOLFERSBERGER MICHAEL G. 《Integrative and comparative biology》1981,21(3):775-791
SYNOPSIS. We propose that particles, 715 nm in diameter,observed on the apical plasma membranes of cation transportingcells of insect midgut, salivary glands, and Malpighian tubulesare modified F1-F0 coupling complexes such as those found onphosphorylating membranes of mitochondria, chloroplasts, andbacteria. We suggest the generic term, portasome, to describeall of these particles and point out that they are located onthe side of the membrane which is electronegative and has thelow cation concentration, i.e., on the input side in each case.Biophysical evidence identifies the portasome bearing membraneas the ion transporting membrane in several insect epithelia,some of which exhibit ion modulated ATPase activity. The activityof a K+-modulated ATPase from Manduca sexta midgut is increasedin portasome enriched plasma membrane fractions. We proposethat portasomes orient the scalar hydrolysis of negatively chargedMgATP2 to less negatively charged MgADP thereby eliminatingthe attraction of MgATP2 to K+ with the result that theK+ ions are ejected to the opposite side of the portasome bearingmembrane. This mechanism explains the coupling of the scalarhydrolysis of ATP to the vectorial active transport of K+ whichleads to the establishment of a K+ electrochemical gradient.The reverse process, but with an H+ ionophore replacing a K+ionophore in the portasome, would provide a mechanism for couplingthe vectorial flow of H+, driven by a proton electrochemicalgradient, to scalar ATP synthesis and thereby provide a mechanismfor oxidative phosphorylation. Electrogenic active potassiumion transport would appear to have evolved from oxidative phosphorylation. 相似文献
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