Fig. 3.

Two different conformational changes, a pH induced and a Li⁺ induced, are reflected by the fluorescence changes of single Trp/F136W and Trp/F339W, respectively. The reaction mixtures were as in Fig. 2, and the fluorescence emission was measured with the time-dependent mode of the spectrofluorimeter. The excitation was at 295 nm and the emission was at the peak of each variant; 344, 335, and 338 nm for Trp-less NhaA, single Trp/F136W, and single Trp/F339W, respectively.