FIGURE 2.

The fluorescence characteristics of purified CFP in solution at 420 nm excitation under varying pH conditions. (a) Comparison of fluorescence emission spectra of CFP at pH 6.5 (dark shading) and at pH 7.5 (light shading). The fluorescence maxima were observed at 486 nm irrespective of the pH levels, though a difference in the contribution of the second peak at 505 nm was observed. (b) The fluorescence decays of CFP at pH 6.0 (shading), 6.5 (dark shading), and 8.0 (light shading). (c) The contributions of the lifetimes τ₁ (solid), τ₂ (shading), and τ₃ (light shading) at the donor emission maximum were calculated from the preexponential factors and plotted as normalized fractional contributions as a function of pH. (d) Mean lifetimes at the donor emission maximum were plotted as a function of pH.