title: Evidence for phase separation in the membrane of an osmotically stabilized fatty acid auxotroph of E. coli and its biological significance.
abstract: 1. An unsaturated fatty acid auxotroph of Escherichia coli accumulated a high content of saturated fatty acids in its membrane when it was cultured under osmotically stabilized conditions. The physicochemical properties of the phospholipid extracts and of the membrane fraction from the cells were investigated by means of proton magnetic resonance, infrared spectroscopy and differential scanning calorimetry. 2. Physicochemical studies indicate that the phospholipid bilayers in the membranes exhibit at least two phase transitions, a minor one at approx. 19 degrees C and a major one at approx. 43 degrees C. Between the two temperatures, gel and liquid crystalline domains co-exist. Moreover, even in the gel state, phospholipids seem to segregated into domains containing different proportions of unsaturated fatty acids. 3. The Arrhenius plot of beta-galactoside transport rates is biphasic. The inflection point is at 22 degrees C. This means that the appearance of the fluid region in the bilayer at approx. 19 degrees C is important in the activation of membrane transport.
mesh_terms: D001692:Biological Transport; D002152:Calorimetry, Differential Scanning; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure*; D004926:Escherichia coli / Q000378:metabolism / Q000648:ultrastructure*; D005231:Fatty Acids, Unsaturated / Q000378:metabolism; D005697:Galactosides / Q000378:metabolism; D008051:Lipid Bilayers; D009682:Magnetic Resonance Spectroscopy; D008563:Membrane Lipids / Q000032:analysis*; D010743:Phospholipids / Q000032:analysis*; D013055:Spectrophotometry, Infrared; D013816:Thermodynamics
chemical_list: D005231:Fatty Acids, Unsaturated; D005697:Galactosides; D008051:Lipid Bilayers; D008563:Membrane Lipids; D010743:Phospholipids