FIGURE 3.

Assignment of 5F-Trp ¹⁹F NMR resonances by site-directed mutagenesis: the empty sugar cleft conformer. Shown are spectra for the wild-type and indicated mutant receptors, each labeled with 5F-Trp. The positions of resonances deleted by mutation are indicated by arrows. All samples contained 100 mM KCl, 10 mM Tris, pH 7.1, 10% D₂O, 0.5 mM CaC1₂, and 75 µM 3F-Phe as an internal frequency reference; spectra were recorded at 470 MHz and 25 °C.