Occupancy of two primary chloride-binding sites in Natronobacterium pharaonis halorhodopsin is a necessary condition for active anion transport.

Abstract

The existence of two primary chloride-binding sites was found on the basis of the study of halorhodopsin spectra at different chloride concentrations. SVD analysis of the spectra revealed two chloride-dependent components at low chloride concentration (0.1-10 mM). Global fitting of SVD components found K(D) values of 0.47 and 5.2 mM with unitity Hill coefficients. The second K(D) coincides with the apparent K(D) of the photovoltage response of halorhodopsin.