Comparison of the RRS of BR with native A1 retinal chromophore and various GPR with MMAR chromophore.

Data was recorded at room temperature using 532-nm laser excitation for GPR:MR, GPR-D97N:MR and GPR-DNFS:MR using 2.8 mW laser power. The BR spectrum, reported previously [75], was recorded using 785-nm excitation. Spectra were not smoothed and were scaled approximately using the intensity of the peaks in the fingerprint region. A background spectrum of the borosilicate capillary and buffer was subtracted from the sample. The BR spectrum is reproduced from ref. [75]. The scale bar shown is for the GPR-DNFS:MR pH 7.3 spectrum and corresponds to 500 counts of Raman scattering intensity. Additional details are given in Materials and Methods.