text: Both the fluorescence excitation and emission spectrums of wild-type EosFP are shifted ~65 nm to the right upon excitation toward the red end of the spectrum.  This spectral change is caused by an extension of the chromophore accompanied by a break in the peptide backbone between Phe-61 and His-62 in an irreversible mechanism. The presence of a crisp isosbestic point at 432 nm also suggests an interconversion between two species.  An absorption peak at 280 nm is visible due to aromatic amino acids which transfer their excitation energy to the green chromophore.  The quantum yield of the green-emitting form of Eos is 0.7.  In the red shifted species, there are pronounced vibronic sidebands separate from the main peak at 533 nm and 629 nm in the excitation spectrum and emission spectrum respectively. There is another peak in the red excitation spectrum at 502 nm likely due to FRET excitation of the red fluorophore. The quantum yield of the red-emitting form is 0.55.
  EosFPs variants show almost no difference in spectroscopic properties, therefore, it is likely that the structural modifications which arise from separation of interfaces have little to no effect on the structure of the fluorophore-binding site.