Photoconversion of various green and cyan fluorescent proteins to the form fluorescing in the red area of the visible spectrum under the oxygen-free conditions was studied. Such photoconversion has earlier been described for the EGFP green fluorescent protein. Phylogenetically distant fluorescent proteins that have a low homology of their amino acid sequences but contain chemically identical chromophores based on a Tyr residue were shown to be susceptible to this type of photoconversion. At the same time, the ECFP protein, which has 92% homology with EGFP but contains a chromophore based on tryptophan did not undergo the photoconversion. Thus, it is precisely the chromophore structure, rather than the amino acid environment that determines the ability of green fluorescent proteins to display photoconversion to the red fluorescent state under anaerobic conditions.