Fig. 4. Characterization of purified wtGR and GR1 in detergent micelles shows that GR1 has a chloride binding site and is also sensitive to bromide, iodide, and nitrate. Fluorescence spectra of ∼3 μM (A) wtGR and (B) GR1 in the presence of 0 (bold), 12.5, 25, 50, 100, 200, 300, and 400 mM (red) sodium chloride. Insets: integrated emission response (y-axis) to sodium chloride. (C) Integrated emission response of ∼3 μM GR1 to 0 mM (Fi, Ctrl) or 400 mM (Ff) sodium chloride, bromide, iodide, nitrate, or dihydrogen phosphate. All spectra were acquired in 50 mM sodium acetate buffer containing 600 mM sodium gluconate at pH 5. Excitation for the rhodopsin was provided at 530 nm, and the emission was collected and integrated from 600–800 nm. The average of three technical replicates with standard error of the mean is reported.
