Characterization of human serum immunoglobulin g modified with singlet oxygen.

Reactive oxygen species, as singlet oxygen ((1)O2), is continuously being generated by aerobic organisms, and react actively with biomolecules. At excessive amounts, (1)O2 induces oxidative stress and shows carcinogenic and toxic effects due to oxidation of lipids, proteins and nucleic acids. In our study, immunoglobulin G (IgG) was modified by (1)O2 generated by the ultraviolet (UV) irradiation of methylene blue. The modified IgG was characterized by UV spectroscopy, carbonyl content determination, thermal denaturation and electrophoretic study. Oxidation induced by modification of IgG by (1)O2 also analyzed by scavenging studies. It was found that ultraviolet absorption spectra of modified IgG shows marked hyperchromicity. The carbonyl content was found to be high in modified IgG as compared to native IgG which confirms its oxidation. Thermal denaturation of modified protein sample shows decrease in Tm value by 3 °C and less intensity banding pattern on polyacrylamide gel electrophoresis. The quenching effect of sodium azide provides clue for modification of IgG by methylene blue, as it is known (1)O2 scavenger. Hence, the IgG modified with (1)O2 may be one of the etiological pathogenic factors for rheumatoid arthritis and diabetes.