Photophosphorylation in Alkalophilic Halobacterial Cells Containing Halorhodopsin: Chloride-Ion Cycle?

A. V. Avetisyan, A. D. Kaulen, V. P. Skulachev^*, and B. A. Feniouk

Department of Bioenergetics, Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119899 Russia; fax: (095) 939-3188; E-mail: skulach@head.genebee.msu.su

^* To whom correspondence should be addressed.

Received December 10, 1997; Revision received January 30, 1998

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Light-driven ATP synthesis is found in cells of the alkalophilic bacterium Natronobacterium pharaonis containing halorhodopsin but deficient in H⁺-pumping bacteriorhodopsin. Photophosphorylation occurs with cyanide-inhibited respiratory chain as well as without cyanide in conditions with low Cl^- concentration in the incubation medium. Increase in Cl^- concentration from 0.1 to 2.35 M in the incubation medium leads to inhibition of photophosphorylation. Continuous illumination increases membrane DeltaPsi if respiration is inhibited by cyanide. This effect is stimulated by DCCD, an ATPase inhibitor. These data can be explained if one suggests that halorhodopsin pumps Cl^- into the cells whereas Cl^- release from the cells through Cl^--ATP-synthase is coupled with the ATP synthesis (chloride-ion cycle).

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KEY WORDS: chloride-ion cycle, halorhodopsin, alkalophilic bacterium, Cl^--ATP-synthase

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