Effeсts of the 70th Amino Acid Residue on the Photostability of FAST Complexes

We report a novel mutant of FAST–FAST T70V. The fluorescent properties of the complex were studied to show that the T70V mutation only slightly affects the fluorescent properties but has no effect on the photostability of the protein–fluorogen complex. Thus, evidence was obtained showing that the threonine alcohol group is not involved in the irreversible photodegradation of the complex, despite the possible contact of the amino acid with the fluorogen.