Portasomes as Coupling Factors in Active Ion Transport and Oxidative Phosphorylation |
| |
Authors: | HARVEY WILLIAM R; CIOFFI MOIRA; WOLFERSBERGER MICHAEL G |
| |
Institution: | Department of Biology, Temple University Philadelphia, Pennsylvania 19122 |
| |
Abstract: | 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. |
| |
Keywords: | |
本文献已被 Oxford 等数据库收录! |
|