Cl −-dependent photovoltage responses of bacteriorhodopsin: comparison of the D85T and D85S mutants and wild-type acid purple form

• Published in: FEBS letters 1997-12, Vol.418 (3), p.239-242
• Main Authors: Kalaidzidis, Inna V, Kaulen, Andrey D
• Format: Article
• Language: English
• Subjects: Bacteriorhodopsin; Bacteriorhodopsins - genetics; Bacteriorhodopsins - metabolism; Chlorides - metabolism; Cl − transport; Cl− transport; D85S and D85T mutants; Halobacterium - metabolism; Halobacterium salinarium; halorhodopsin; Ion Transport; Lasers; Mutation; Photic Stimulation; Photocycle; Photovoltage response; purple membrane; Purple Membrane - metabolism
• ISSN: 0014-5793; 1873-3468
• DOI: 10.1016/S0014-5793(97)01390-2

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.