Figure 1.

(a) pH-dependent absorbance of EYFP. (b) pH dependency of fluorescence of various GFP mutants in vitro and in cells. The fluorescence intensity of purified recombinant GFP mutant protein (solid symbols) as a function of pH was measured in a microplate fluorometer as indicated in Materials and Methods. The fluorescence of the Golgi region of HeLa cells expressing either GT-EYFP or GT-EGFP (open symbols) was determined during pH titration with the ionophores monensin/nigericin in high KCl solutions.