ИСТИНА

Amyloid fibrils (AF) accumulation in organs and tissues accompanies many serious diseases, such as Alzheimer's, Parkinson's, etc. A fluorescent dye thioflavin T which changes its photophysical properties when it is incorporated into AF is the most common probe to diagnose the formation of AF and study their structure in vitro. However, the spectral characteristics of ThT do not allow to use it for studying AF in tissues and in vivo. We investigated the photophysical properties (absorption, fluorescence, fluorescence excitation, lifetime of the excited state) of trans-2-[4- (dimethylamino) styryl]-3-ethyl-1,3-benzothiazolium perchlorate (DMASEBT) – a new analogue of ThT. The absorption and fluorescence spectra of the new fluorescent probe have a longwavelength shift in comparison to the ThT spectra. With the use of a specially developed approach based on absorption and fluorescence spectroscopy of solutions prepared by equilibrium microdialysis, it was shown that incorporation of DMASEBT into insulin amyloid fibrils leads to a long-wavelength shift of its absorption and fluorescence spectra and a significant increase of the fluorescence quantum yield of DMASEBT. ThT and DMASEBT interaction with insulin AF have the same stoichiometry. For understanding of the mechanism of DMASEBT incorporation into AF, its spectral properties in the presence of sodium polystyrene sulfonate (PSS) were studied. It is shown that DMASEBT can interact with PSS in the form of monomers and dimers depending on the concentration of PSS. The comparison of spectral properties of the monomeric and dimeric forms of the dye allowed to conclude that the incorporation of DMASEBT into AF occurs in the form of monomers.