CONICET | Buscador de Institutos y Recursos Humanos

Singlet oxygen (1O2) is a very harmful non-radical species that reacts with electron-rich biological molecules. Due to their intrinsic abundance in the biological milieu, proteins are the main targets of action of 1O2, causing structure changes, covalent and non-covalent aggregation, and enzymatic activity losses. Serum albumins (SAs), are fundamental for the maintenance of the oncotic pressure of the plasma and the transporting of small vital molecules and drugs. As well as the functionality of both SA are depending on the protein structure, in this report we evaluated the impact of the 1O2 oxidation on the human (HSA) and bovine (BSA) SAs, which show an amino acid similarity of about 77%, but differing mainly in the number of Trp and Tyr residues, two of the oxidizable residues by 1O2 besides Cys, Met and His. The ruthenium (II) tris(2,2´-bipyridine) cation (Rubpy, 20 μM) was used as photosensitizer for generation of 1O2, since Rubpy does not bind to the SAs (10-100 μM). Photolysis was performed using a 1 W blue LED (443±27 nm) and the oxidation kinetics was monitored by both absorption and fluorescence spectroscopy. Post-irradiation the sensitizer was separated by ion exchange chromatography, and the modified proteins were analyzed by several spectroscopies, laser particle electrophoresis (Z potential), protein electrophoresis (PAGE); carbonyl content and pseudo-esterase activity determination through biochemical techniques. Results indicated the oxidative degradation of Trp residues with the production of carbonylic fluorescent products. The primary structure of the SA was retained, despite changes of the superficial electrical potential and hydrophobicity, and the reduction of the pseudo-esterase activity. Albeit both SAs share similar globular structure and amino acid sequence, the present results indicates subtle differences in the impact of the 1O2-mediated protein oxidation.