Effects of Ubiquinone-10 on the Stability and Mechanical Properties of Lipid Membranes

Sammanfattning: Ubiquinones are a group of fat-soluble molecules present in many biological membranes. The most abundant version in humans, ubiquinone-10 (Q10), plays an important role in the mitochondrial respiration chain and also functions as a powerful antioxidant. Accumulating evidence suggests that Q10 also could have other functions in the membrane. The aim of this thesis has been to explore Q10’s possible role as a membrane stabilizer.To investigate the potential effect of Q10 in membranes, liposomes with compositions of biological relevance were used as models systems. In lipid systems mimicking that of the inner membrane of the mitochondria, Q10 was found to lower the membrane’s permeability to hydrophilic solutes, render the membrane more resistant to rupturing and promote membrane lipid order. In models mimicking the plasma membrane of E.coli, Q10 was observed to decrease the water permeability and increase the elastic resistance against membrane deformation during osmotic shock. All in all, the results suggest a general membrane stabilizing effect of Q10. The results indicate, however, that the extent of, as well as the mechanisms behind, the membrane stabilizing effects of Q10 vary depending on the membrane lipid composition. Part of the reason for this can likely be traced back to differences in the intermembrane location of Q10.Supplementary experiments, which facilitated the investigations of Q10 membrane effects, revealed that the choice of cuvette material was of importance for liposome leakage experiments with fluorescent hydrophilic dyes. The results of these experiments highlight the need to take liposome-cuvette interactions into account when planning and evaluating spectroscopic studies involving liposomes.