Physical properties of membrane lipids: biological relevance and regulation.

Introduction..................................................................... 232 Pertinent Properties of the Cell Envelope ......... ............................. 233 E. coli Fatty Acid Auxotrophs .............. ................................... 233 Specific inhibitors of Fatty Acid Synthesis ......... ............................ 234 LIPID BILAYER PHASE PROPERTIES ........ ............................ 234 Empirical Rules Deduced from Model Systems ........ ......................... 234 Physical Properties of the E. coli Membrane Lipids ....... ..................... 236 Phase transitions............................................................ 236 (i) X-ray diffraction ......................................................... 236 (ii) DSC ..................................................................... 237 (iii) Fluorescent probes ..................................................... 237 (iv) Spin labeling .............. ............................................. 237 Phase separations. (i) Physical studies ......... .............................. 237 (ii) Freeze-fracture electron microscopy ...................................... 239 Lateral movement of lipids ............... ................................... 240 CORRELATIONS BETWEEN MEMBRANE-ASSOCIATED PHYSIOLOGY AND LIPID PHYSICAL PROPERTIES ........ ............................ 240 General Physiology ............................................................ 240 Lactose Transport System ................ ..................................... 240 Relevant properties of lactose transport system ....... ....................... 240 Transport system induction and lipid synthesis ....... ........................ 241 Transport and lipid phase changes ........... ................................ 241 Other Transport Systems .................. .................................... 243 Sugar transport systems ................ ..................................... 243 Amino acid transport systems ............. .................................. 243 Other Physiological Processes ................................................ 243 Lipid requirement for alkaline phosphatase derepression ...... .............. 243 Chemotaxis ............. . .................................................... 244 Initiation of DNA synthesis ............... ................................... 244 Methylgalactoside permease induction ......... .............................. 244 Cell integrity ................. ............................................... 244 Enzymatic activity ........................................................... 244 Requirement for Lipids with Specific Physical Properties ...... ................ 245 Requirement for membrane liquidity ......................................... 245 Minimum UFA content...................................................... 246 Minimum saturated fatty acid content ......... ............................... 246 Significance of temperature-induced alterations in fatty acids ..... ........... 247 REGULATION OF LIPID PHYSICAL PROPERTIES ........................... 247 Possible Lipid Alterations Producing Altered Phase Transitions ..... ........... 247 Sites of Control ................................................................ 247 In Vitro Studies ............................................................... 247 (i) Acyltransferase specificity ............. ................................... 248 (ii) Fatty acid synthetase ................ .................................... 249 In Vivo Studies ................................................................ 249 (i) Determination of fatty acid chain length ........ ........................... 249 (ii) Regulation of the saturated-to-unsaturated fatty acid ratio ..... ........... 250 (iii) Temperature control of fatty acid composition ....... ..................... 250 CONCLUSION.................................................................. 251 LITERATURE CITED .............. ............................................ 252