Cl- -dependent photovoltage responses of bacteriorhodopsin: comparison of the D85T and D85S mutants and wild-type acid purple form.
Laser flash-induced photovoltage responses of the D85S and D85T mutants as well as of the wild-type acid blue form are similar and reflect intraprotein charge redistribution caused by retinal isomerization. The Cl- -induced transition of all of these blue forms into purple ones is accompanied by the appearance of electrogenic stages, which is probably associated with Cl- translocation in the cytoplasmic direction. Cl- translocation efficiency of these purple forms is much lower than that of the proton transport by the wild-type bacteriorhodopsin. The values of the efficiency do not exceed 15, 8 and 3% for the D85T, D85S and wild-type acid purple form, respectively. Cl- induces an additional electrogenic phase in the photovoltage responses of the D85S mutant and the wild-type acid purple form. This phase is supposed to be associated with the reversible Cl- movement in the extracellular direction. It is interesting that this component is absent in the photovoltage response of the D85T mutant which has, like halorhodopsin, a threonine residue at position 85.
Kalaidzidis
I V
IV
Department of Photobiochemistry, A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Russia.
Kaulen
A D
AD
D001436:Bacteriorhodopsins / Q000235:genetics / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism*; D006217:Halobacterium / Q000378:metabolism; D017136:Ion Transport; D007834:Lasers; D009154:Mutation; D010775:Photic Stimulation; D018717:Purple Membrane / Q000378:metabolism*
D002712:Chlorides; D001436:Bacteriorhodopsins