Fig. 3.

Photoactivation of EGFP-66Qui results in abFP that fluoresces at acidic pH only. (A) A photograph of EGFP-66Qui protein samples before and after illumination with a handhold UV lamp (365 nm). (B) Absorption spectral change of EGFP-66Qui upon photoactivation in phosphate buffer (100 mM, pH 7.4). (C) Fluorescence emission spectra of photoactivated EGFP-66Qui in buffers with indicated pH values. (D) pH profile of photoactivated EGFP-66Qui. Fluorescence emission intensity at 560 nm measured in c was plotted against pH. (E) Extinction coefficient (ε, measured at 523 nm) and quantum yield of photoactivated EGFP-66Qui at different pH. Relative brightness is the product of these two values normalized to that at pH 7.4. (F) Fluorescence images of bacterial pellets expressing EGFP-66Qui before and after photoactivation in different pH aqueous media. Adapted with permission from Fu, C. et al. (2018). Genetically Encoding Quinoline Reverses Chromophore Charge and Enables Fluorescent Protein Brightening in Acidic Vesicles. Journal of the American Chemical Society, 140, 11058–11066. Copyright (2018) American Chemical Society.