A second mechanism for sodium extrusion in Halobacterium halobium: a light-driven sodium pump. |
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Authors: | E V Lindley R E MacDonald |
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Institution: | Section of Biochemistry, Molecular and Cell Biology Cornell University, Ithaca, New York 14853 USA |
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Abstract: | Membrane vesicles from a red mutant of R1 accumulate protons when illuminated causing the pH of the suspension to rise. Sodium is extruded from the vesicles and a membrane potential is formed. This potential and the proton uptake are abolished by valinomycin if K+ is present. In contrast, Na+-efflux is uninhibited by valinomycin even though no membrane potential is detectable and H+ influx does not occur. (hexafluoracetonyl)acetone (1799) stimulates proton uptake but does not abolish membrane potential. We propose that a light-dependent sodium pump is present. Passive proton uptake occurs in response to the electrical gradient created by this light-driven Na+ pump in contrast to the proton, and passive Na+ flux that occurs in response to the light-driven proton pump described in vesicles of the parent strain of R1. |
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Keywords: | DCCD N N′-dicyclohexyl-carbodiimide 1799 bis(hexafluoracetonyl)acetone Hepes N-2-hydroxy-ethyl piperazine-N′-2-ethanesulfonic acid Δψ the electrical potential difference CCCP SF6847 |
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