EFFECT OF POLYUNSATURATED FATTY-ACID DEFICIENCY ON DIPOLE RELAXATION IN THE MEMBRANE INTERFACE OF RAT-LIVER MICROSOMES

The influence of a Eat-free diet on the lipid dynamics of rat liver mi crosomes and liposomes of microsomal lipids was studied by using diffe rent fluorescence methods. Lifetime distribution and rotational diffus ion of probes with different localization in the lipid bilayer were me asured using multifrequency fluorometry. Lateral mobility was studied by measuring excimer formation of pyrenedodecanoic acid. Dipolar relax ation in the interfacial region was studied using 2-dimethylamino-6-la uroylnaphthalene (Laurdan). in spite of large changes in the fatty aci d composition of microsomal lipids, polyunsaturated fatty acid deficie ncy showed no effect on the lifetime distribution and rotational mobil ity of 1,6-diphenyl- 1,3,5-hexatriene (DPH), -(trimethylamino)phenyl)- 6-phenyl-1,3,5-hexatriene (TMA-DPH), 2-, 7- and 12-(9-anthroiloxy)stea ric acids. The treatment did not change the lateral diffusion of pyren edodecanoic acid, either. However, generalized polarization of Laurdan fluorescence was higher in polyunsaturated fatty acid deficient micro somes as compared to the polyunsaturated fatty acid sufficient ones. T his effect was also observed in liposomes of the total microsomal lipi ds, indicating that the changes in fatty acid composition resulting fr om polyunsaturated fatty acid deficiency produced a small but signific ant decrease in the rate of dipolar relaxation in the region of the li pid polar groups of the bilayer. The absence of lipid gel phase domain s in rat liver microsomes was also indicated by Laurdan fluorescence f eatures.