The binding of bovine serum albumin with dye molecules at different pH values. Fluorescence lifetime studies

Abstract

The spectral and kinetic characteristics of the fluorescence of the solutions of bovine serum albumin (BSA) and the dyes (N-(p-carboxyphenyl) imide of 4-(dimethylamino) naphthalic acid (CAPIDAN) and Bengal Rose (BR)) in BSA solutions were studied at 3.5 < pH < 8.0. It was discovered that the attenuation of CAPIDAN fluorescence at the studied pH region is described by the sum of three components (with the values of time constants: 6.0 ns < τ 1 < 8.5 ns, 1.8 ns < τ 2 < 2.2 ns, 0.4 ns < τ 3 < 0.6 ns), while it is described by two components for BR (0.33 ns < τ 1 < 0.4 ns, 2.0 ns < τ 2 < 3.1 ns). It is shown that the mechanisms of the binding of dye and protein molecules are different for CAPIDAN and BR. The binding process of CAPIDAN and BSA is regulated by the conformation of the binding center. The interaction between the BR and BSA molecules is electrostatic, the magnitude of this interaction is determined by the ratio of the charges of the dye and protein molecules. The dependence of the wavelength of the maximum of the spectra, the intensity of the glow and the efficiency of quenching of the fluorescence of the molecules of the studied dyes on the pH is analyzed. The parameters dμ, which characterizes the change in the dipole moment of the fluorophore during its excitation, and η, which characterizes the change in the intensity at the maximum of the fluorescence spectrum at different pH solutions, were also determined for BR. The following ratios were determined at the studied pH range: and η < 1. The changes of the characteristics of the stationary fluorescence of the studied dyes at different pH of BSA solutions confirm the mechanisms of the binding between CAPIDAN or BR molecules and protein molecules.