ИСТИНА

Actin is the most abundant protein in eukaryotic cells. Previously, we have shown that the so-called inactivated actin, which for a long time was considered to be an intermediate state in the pathway of protein unfolding, actually is a monodisperse ordered aggregate, binding ANS. This study aimed to determine the parameters of ANS binding to inactivated actin. It was shown that, despite of a significant increase in fluorescence intensity and blue shift of the fluorescence spectrum (from 530 nm to 470 nm) of ANS solution in the presence of inactivated actin, its absorption spectrum did not change, though fluorescence excitation spectrum was red shifted (λmax = 385 nm) as compared with that of free dye (λmax = 340 nm). It was shown that the position of fluorescence excitation spectrum and fluorescence spectrum of ANS solution in the presence of inactivated actin changed even at low concentrations of protein and remained unchanged with further increase in protein concentration, while the fluorescence intensity increased linearly. These data suggest that in solution of ANS in the presence of inactivated actin, there are always two kinds of dye molecules: free dye and dye interacting with protein, which differ by fluorescence and absorption spectra. The quantity of ANS molecules interacting with protein is so small that it does not have any effect on the absorption spectrum of the solution, but due to the high fluorescence quantum yield of these molecules they determine its fluorescence and fluorescence excitation spectra.