Fig. 2.

a, Absorbance changes of sensory rhodopsin (sR) at 375 and 580 nm induced by red background light. The sample was a suspension of Flx3R vesicles, prepared vesicles, prepared and regenerated in a 3 × 3 mm quartz cuvette clear on four sides with all-trans retinal as described¹⁰. The regeneration of sensory rhodopsin was monitored as described¹⁰, use of the regenerated system permitting precise quantitation of the sensory rhodopsin content. Flx3 vesicles containing native sensory rhodopsin gave the same phototransients as the regenerated protein in Flx3R shown here. Flash-induced absorbance changes were measured as described⁹. Background excitation was provided by a tungsten halogen lamp beam passed through a long pass Corning 2–61 (cutoff 610 nm) and Ditric Optics 700 nm short pass filter combination and applied to the sample at 90° with respect to the measuring beam. The maximum red light intensity (I_max) was 4.25 × 10⁶ erg cm⁻² s⁻¹. The inset shows the light intensity-dependence of the absorbance changes at 375 nm (ΔA₃₇₅). b, Spectrum of S₃₇₃ and sR₅₈₇. The latter is the spectrum obtained by regeneration of sensory rhodopsin apoprotein with all-trans retinal⁹ and the former was calculated by adding the sR₅₈₇ spectrum to the light-induced difference spectrum obtained using the system described in a. The extinction coefficients are based on our measurements^9,10 and have absolute uncertainty of ±15%.