Kinetics of radiation- and cytochrome c-induced modifications in liposomes analysed by FT-Raman spectroscopy

Fourier transform Raman spectroscopy on artificial lipid membranes was used to study radiation-induced peroxidation processes as a function of time after radiation exposure. The time dependent intensity changes of the Raman lines of various C=C bondings were compared to results obtained by measuring conjugated dienes and by the thiobarbituric acid test for malondialdehydes. The results show that mainly the cis C=C bonds of the lipid chains are involved and, therefore, indicate that gamma-radiation induces conformational changes in the lipid chain while the mobility of the lipid chains is reduced. New Raman bands can be assigned to aldehyde products induced at the end of the peroxidation process. The immediate decrease of the =CH vibration lines was directly correlated with the formation of conjugated C=C double bonds suggesting that these vibration lines are in contrast to the C=C lines solely Raman active, when isolated C=C bonds are present. Cytochrome c (ox.) incorporated into the bilayer of the artificial membranes induced autooxidation processes not influenced by gamma-radiation. It was observed that cytochrome c (ox.)-induced changes of the relative intensity of the C=C bonds differ from those induced by gamma-radiation. These results of cytochrome c together with the inhibitory effects of the antioxidant alpha-tocopherol suggest that the radical species involved in the cytochrome c induced process might be different from the free radicals involved in the gamma-radiation-induced process.