¹⁹F NMR showed propofol binding to the transmembrane domain intrasubunit pocket of pentameric ligand-gated ion channel from Erwinia chrysanthemi (ELIC) only in the resting state. (A and B) The agonist propylamine (18 mM) binding (green) broadened the ¹⁹F NMR linewidths of sites 265 and 308 compared with the linewidths in the absence of agonist (blue). (C and D) The addition of propofol (120 μM) caused downfield shift and approximately 50-Hz increase in the linewidth of the ¹⁹F NMR peaks (red) compared with that in the apo ELIC (blue). (E and F) Under desensitized conditions (green), no change was observed in the ¹⁹F NMR spectra upon the addition of propofol (orange). (G) Temperature dependence of the ¹⁹F chemical shift for site 265 in the absence (blue) and presence (red) of propofol. (H) Temperature coefficients calculated based on the experiments as shown in (G) for sites 265 (magenta) and 308 (cyan) in the absence (solid) and presence (hash) of propofol. PFL = propofol.