Fig. 3. Spectral difference between the high-F⁻ sample and the F⁻-free sample.

(A) Direct ¹⁹F-detected ssNMR spectra of high-F⁻ sample (black) and F⁻-free sample (red). Comparison of 2D NCA (B) and NCOCA (C) spectral close-ups of residues (marked as a black font) with a notable signal intensity decrease in the F⁻-free sample compared to the high-F⁻ sample. (D) The signal-to-noise ratio of the NCA spectrum is shown as a histogram, and loop 1 (R₂₅FNPLHQAIPL₃₅) is indicated. A.U., arbitrary unit. (E) Residues with notably decreased signals are shown in magenta on the structure model.