I.A. Sergeeva, G.P. Petrova, Moscow State University, Russia
A method used in this work bases on polarization of fluorescence upon the laser excitation in the ultraviolet (UV) wavelength range. This method was exploited to study toxic effects of lead, potassium, rubidium and cesium ions over water solutions of bovine serum albumin (BSA) and γ-globulin. All studies were performed at the isoelectric points of serum albumin (pH 4,9) and γ-globulin (pH 6,0).
Preliminary, there were obtained fluorescence spectra of the tryptophan amino acid water solutions in the presence of the Pb2+ ions. It should be noted, that fluorescence intensity of tryptophan is not effected by the concentration of the lead salt, even when there is a tenfold exceed of it over the concentration of amino acid.
In our earlier works [1,2] fluorescence spectra of BSA were studied in water solutions containing NaCl and KCl salts. It was found that Na+ ions do not alternate intensity of albumin fluorescence spectrum, whereas K+ ions cause decrease in fluorescence intensity.
In BSA and γ-globulin water solutions the presence of Na+ ions (with concentration ca. the physiological value) does not effect polarization degree of fluorescence, but the degree increases when adding Pb2+, Cs+, Rb+ or K+ ions (with concentrations ca. MPC). This phenomenon indicates the changes in dynamic properties of proteins macromolecules such as the correlation time of rotational mobility and, consequently, the mass of the particles.
These results draw to a conclusion that fluorescence quenching occurs only in case when amino acid is a part of protein compound. This effect is due to the facts that lead, potassium, rubidium and cesium ions are strongly associated with negative groups on protein surface, and that the nature of macromolecules interaction changes resulting in protein clusters formation.
Moscow State University
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