[Effect of the unsaturation of lipids fatty acids on the structure and function of the cytoplasmic membranes of E. coli].

The results presented in this paper establish relationships between structural, morphological and functional properties of cytoplasmic membrane vesicles isolated from an E. coli unsaturated fatty auxotroph. The membranes were isolated from cells grown in the presence of either oleic, linolenic or elaidic acids. High-angle X-ray diffraction studies show that order-disorder transitions induced by temperature variation sand associated with the hydrocarbon chains of the lipids are a function of the fatty acid composition of the membranes. In some cases, "cocrystallization" of various lipid species takes place within a single type of ordered domains. In other cases, there is a segregation of various lipid species into more than one distinct type of ordered domain. The various order-disorder transitions observed, induce morphological changes in the hydrophobic core of the membranes which can be detected by freeze-fracture electron microscopy. A random distribution of particles on the fracture faces is observed when the hydrocarbon chains of the lipids are disordered. Upon ordering of the hydrocarbon chains, particles are excluded from the ordered domains and as a consequence, smooth areas and areas with dense ly packed particles are observed. Discontinuities in the rate of energy-dependent beta-galactoside uptake as a function of temperature correlate with the order-disorder transitions observed. The increased slope of the Arrhenius representation in the temperature region of the transition is associated with the segregation of the carrier proteins excluded from the ordered membrane domains and their subsequent aggregation in the membrane domains containing the disordered lipids.