Fig. 4: Na⁺ increases heterogeneity in the selectivity filter.

Overlays of selectivity filter (SF) peaks from (a) ¹H–¹³C HMQC and (b) TROSY-HSQC spectra of NaK in 600 mM Na⁺ (red) and 100 mM K⁺ (black). Stereospecific assignments based on NOESY data are given where possible.