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Biophys J, October 2002, p. 1749-1759, Vol. 83, No. 4

Clminus Concentration Dependence of Photovoltage Generation by Halorhodopsin from Halobacterium salinarum

Eiro Muneyuki,* Chie Shibazaki,dagger Yoichiro Wada,dagger Manabu Yakushizin,dagger and Hiroyuki Ohtanidagger

 *Chemical Resources Laboratory (Research Laboratory of Resources Utilization), Tokyo Institute of Technology, Yokohama 226-8503, and  dagger Department of Biomolecular Engineering, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Yokohama 226-8501, Japan

The photovoltage generation by halorhodopsin from Halobacterium salinarum (shR) was examined by adsorbing shR-containing membranes onto a thin polymer film. The photovoltage consisted of two major components: one with a sub-millisecond range time constant and the other with a millisecond range time constant with different amplitudes, as previously reported. These components exhibited different Cl- concentration dependencies (0.1-9 M). We found that the time constant for the fast component was relatively independent of the Cl- concentration, whereas the time constant for the slow component increased sigmoidally at higher Cl- concentrations. The fast and the slow processes were attributed to charge (Cl-) movements within the protein and related to Cl- ejection, respectively. The laser photolysis studies of shR-membrane suspensions revealed that they corresponded to the formation and the decay of the N intermediate. The photovoltage amplitude of the slow component exhibited a distorted bell-shaped Cl- concentration dependence, and the Cl- concentration dependence of its time constant suggested a weak and highly cooperative Cl--binding site(s) on the cytoplasmic side (apparent KD of ~5 M and Hill coefficient >= 5). The Cl- concentration dependence of the photovoltage amplitude and the time constant for the slow process suggested a competition between spontaneous relaxation and ion translocation. The time constant for the relaxation was estimated to be >100 ms.

Biophys J, October 2002, p. 1749-1759, Vol. 83, No. 4
© 2002 by the Biophysical Society   0006-3495/02/10/1749/11  $2.00


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Z. Balint, M. Lakatos, C. Ganea, J. K. Lanyi, and G. Varo
The Nitrate Transporting Photochemical Reaction Cycle of the Pharaonis Halorhodopsin
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[Abstract] [Full Text] [PDF]


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