Slowly cycling rhodopsin

Illumination of whole H. halobium cells under anaerobic conditions (to exclude contributions from respiration) produces increased proton motive force, as expected from the functioning of bacteriorhodopsin as a proton pump and of halorhodopsin 

The extrusion of Na, together with uptake, results in lowered intracellular sodium concentrations in energized cells relative to that in the medium. The concentration gradient will slowly eollapse during starvation conditions, but becomes reestablished during illumination [72], The mechanism of sodium transport 

When the only cation present is Na the illumination results in volume decrease [97,388,402], a consequence of active sodium extrusion and passive chloride efflux due to the membrane potential created. When is also added, in order to create conditions similar to those which the cells face during growth, the volume decrease is less because potassium is taken up [402], In envelope vesicles the permeabihty of 

2 Kushner, D.J. (1978) In Microbial Life in Extreme Environments (Kushner, D.J., ed.) pp. 317-368, Academic Press, London. 

10 Oesterhelt, D. and Krippahl, G. (1983) Ann. Microbiol. (Inst. Pasteur) 134B, 137-150. 

---

Slowly, arrestin dissociates, rhodopsin is dephosphorylated, and all-frares-retinal is replaced with 11-cis-retinal. Rhodopsin is ready for another phototransduction cycle. 

---