FIGURE 3.

Selected deuterium NMR spectra for two labeled alanines (7 and 9) in GWALP23-H12 in DOPC bilayers, hydrated with 10 mm buffer at the indicated pH, showing (A) β = 90° and (B) β = 0° sample orientations. The difference in spectra from sharp, well resolved signals above pH 4, to spectra with multiple signals below pH 2.5, indicates that the His¹² residue is charged only under strongly acidic conditions. Red stars in B indicate signals with large |Δν_q|, which likely correspond to backbone Cα-D nuclei of labeled alanine residues. The peptide/lipid ratio is 1/60 at a temperature of 50 °C.