FIGURE 4.

EPR spectra of R1 nitroxide side chain labeled at residue S155C of SRI-HtrI_1-147 wild type and mutants. The structure of the R1 probe (1-oxyl-2,2,5,5-tetramethylpyrroline-3-methyl)-methanethiosulfonate is shown in the inset. Spectra from wild-type complex in the dark state are shown in black for each pair of spectra. In the uppermost pair of full spectra, the spectrum from the light-activated state is shown in red. H166S (green) and R215W (blue) exhibit outermost peaks shifted in opposite directions relative to those of the dark wild-type complex. All spectra were recorded in reconstituted HPL-liposomes at ambient temperature. The outermost peaks are expanded above each spectrum. is defined as the distance between the outermost peaks.