FIGURE 3.

Holo-Y75A UV-visible and resonance Raman spectra, at pH ranging from 5.1 to 10. A, top panel, UV-visible spectra. Arrows indicate the direction of the absorbance change as the pH is increased. The inset shows all data points at the indicated wavelengths and titration curves calculated by global nonlinear least squares analysis. Bottom panel, component spectra obtained from a global fit of all 22 pH titration spectra of holo-Y75A. The black line is the acidic component; the red line is the intermediate pH component; the blue line is the alkaline species. Inset, species distribution as a function of pH obtained from the global fit. ■, the acidic component; ●, the intermediate pH component; ▴, the alkaline species. B, Soret-excited high frequency; C, low frequency rR spectra at the indicated pH values.