Fig. 3: Spectroscopic characterization of ErNaR.
From: A subgroup of light-driven sodium pumps with an additional Schiff base counterion
a Normalized absorption spectra of ErNaR at acidic (pH 4.3) and neutral (pH 8.0) conditions. The spectra have been normalized to the absorbance at 280 nm. b 2D-contour plot of a fs-TA measurement of ErNaR (pH 8.0, 0 mM NaCl). The timescale is linear until 1 ps and logarithmic afterwards. The signal amplitude is color coded as follows: positive (red), no (white) and negative (blue) abs. The mentioned abbreviations represent excited-state absorption (ESA), ground-state bleach (GSB) and stimulated emission (SE). c 2D-contour plot of a flash photolysis measurement of ErNaR (pH 8.0, 1000 mM NaCl). Due to spectral similarity, the region of the O1 and O2 intermediates is indicated as O1/2. The SBS abbreviation represents the “second bright state” signal at 335 nm being a marker of the 13-cis retinal configuration30,31. d Sodium dependence of the transient at 620 nm, indicative of the O1 and O2 intermediates, at pH 8.0. Transients have been normalized to have the same Δabs. at 0.1 ms. The absorption maximum of the O1 and O2 intermediates was plotted against the sodium concentration and the resulting data was fitted with the Hill equation to obtain the sodium dependence of the O1 and O2 intermediates. e Schematic model of the ErNaR photocycle at pH 8.0, 1000 mM NaCl. f 2D-contour plot of a flash photolysis measurement of ErNaR (pH 4.3, 1000 mM NaCl). The SBS abbreviation represents the “second bright state” signal at 335 nm being a marker of the 13-cis retinal configuration. g Sodium dependence of the transient at 600 nm, representative for the O1 and O2 intermediates, at pH 4.3. Transients have been normalized to have the same Δabs. at 0.1 ms. h Schematic model of the ErNaR photocycle at pH 4.3, 1000 mM NaCl.
