Study of the interaction between xylazine and bovine serum albumin by fluorescence quenching measurements.

The binding of xylazine to bovine werum albumin (BSA) was studied by fluoresence quenching, as a function of temperature. The experimental data could be fitted to both the Stern-Volmer equation and the Stern-Volmer equation modified by Lehrer. The temperature dependence of the Stern-Volmer constant, Ksv suggests that the mechanism of the quenching process is mainly dynamic in origin. The thermodynamic parameters were estimated based on such temperature dependence. The positive values found for the enthalpy and entropy changes seem to indicate that the hydrophobic contribution is the predominant intermolecular force stabilizing the xylazine-BSA complex. Fluorescence quenching was also used to calculate the binding constants by the Scatchard procedure. The values of these constants are of the same order of magnitude as the Stern-Volmer constants. These results, together with the spectral changes in the fluorescence emission spectra of BSA induced by xylazine, suggest that the interaction may take place in subdomains IIA and IIIA since these subdomains have been proposed to bind drugs and other hydrophobic materials.