text: The red chromophore, which is generated by cleavage of the peptide backbone, has an absorption maxima at 571 nm and an emission maxima at 581 nm, in its anionic form. The break in the peptide backbone that leads to this chromophore is between His-62 Nα and Cα. The observed red fluorescence occurs due to an extension of the chromophore's π-conjugation where the His-62 imidazole ring connects to the imidazolinone. The hydrogen bond patterns of the red and green chromophores are almost identical.