Fluorescence emission spectra of green fluorescent protein (GFP) showing fluorescence resonance energy transfer (FRET) between tryptophan (Trp57) and cyclic chromophore.

Figure 4. Fluorescence emission spectra (AU, arbitrary units) of green fluorescent protein (GFP) showing fluorescence resonance energy transfer (FRET) between tryptophan (Trp57) and cyclic chromophore. GFP in aqueous buffer (50 mM PBS) and lyophilized powder of GFP. These fluorescence emission spectra were recorded with excitation at 295 nm using excitation and emission slit widths of 2 nm and 5 nm, respectively.