抄録
Dielectric dispersion analysis (DDA) method was selected to the evaluation for variation of membrane properties of liposome and proteoliposomes (liposomes in the bilayer of which membrane protein is incorporated) under stress condition. For DDA, we measured dielectric spectra and performed fitting analysis with two-type function of Debye's equation against the spectra, and we obtained a characteristic frequency observed around 50 MHz (fc2), which is one of the fitting parameters and corresponds to an extent of the rotational motions of lipid molecules. The change of membrane properties of the liposome was first investigated in the liposome suspension with hydroperoxide in order to investigate the effect of oxidative stress. 1-Stearoyl-2-arachidonyl-sn-glycero-3-phosphocholine (SAPC) was herewith used as an easily-oxidizing phospholipid. In the case of SAPC liposome, the decrease of the fc2 value was observed, suggesting the restriction of molecular motion of the surface of SAPC liposome by the oxidation of the SAPC in the presence of hydroperoxide. The stress response of proteoliposome incorporated (Na+, K+)-ATPase as a membrane protein was secondly analyzed in the SAPC liposome solution. Compared with the fc2 value of liposome without the membrane protein, the fc2 value of proteoliposome was found to be small, probably, due to the restriction of lipid molecules by the incorporation of and interaction with the membrane protein. A significant decrease of the fc2 value was also observed under the heat and oxidative stress, together with the hydrolysis activity of ATPase. Based on the above results, the molecular motion of lipid on the liposome surface was found to be analyzed under stress conditions, even in the presence of membrane protein.
