FIGURE 6.
Holo-H32A UV-visible and resonance Raman spectra, at pH ranging from ∼5.3 to 10.5. A, top panel, UV-visible spectra (the arrow indicates the direction of the absorbance change as the pH is increased). Inset, Soret absorbance (A404 nm) versus pH; points are experimental absorbances, and the solid line is the titration curve calculated by global nonlinear least squares analysis. Bottom panel, component spectra obtained from a global fit of all 21 pH titration spectra of holo-H32A. The black line is the acidic component; the dotted red line is the alkaline species. Inset, species distribution as a function of pH obtained from the global fit. ■, the acidic component; ●, the alkaline species. B, high frequency; C, low frequency rR spectra (413.1 nm excited) at the indicated pH values.