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Light-dependent cation gradients and electrical potential in Halobacterium halobium cell envelope vesicles
Federation Proceedings
|May 1, 1977
Summary
Halobacterium halobium vesicles use light energy to create a pH gradient, driving sodium (Na+) efflux against its electrochemical gradient. This coupled ion movement energizes amino acid transport.
Area of Science:
- Microbiology
- Biochemistry
- Membrane Biology
Background:
- Halobacterium halobium utilizes bacteriorhodopsin for light-driven proton (H+) extrusion.
- Cell envelopes can form vesicles retaining functional bacteriorhodopsin.
Purpose of the Study:
- To investigate the mechanism of sodium (Na+) efflux from H. halobium vesicles.
- To understand the coupling between light-induced proton gradients and Na+ transport.
Main Methods:
- Preparation of vesicles from H. halobium cell envelopes.
- Measurement of pH gradients and electrical potentials across vesicle membranes.
- Analysis of Na+ depletion rates under illumination.
Main Results:
- Illumination of vesicles generated a pH gradient and an electrical potential (90-100 mV, interior negative).
- Sodium (Na+) efflux occurred against its electrochemical potential, suggesting active transport.
- Evidence indicates a H+/Na+ exchange mechanism with a stoichiometry greater than 1.
Conclusions:
- Light-induced proton gradients are coupled to active sodium extrusion in H. halobium vesicles.
- The generated sodium gradient is crucial for energizing active amino acid transport.