A confirmation of the phase behavior of Escherichia coli cytoplasmic membrane lipids by x-ray diffraction

Abstract

The lipid fatty acid composition of the cytoplasmic membranes of E. coli can be varied by growing an unsaturated fatty acid auxotroph in the presence of different fatty acid supplements. ESR studies of spin-label partitioning into the cytoplasmic membranes of different lipid fatty acid compositions as a function of temperature were interpreted as indicating a broad order-to-disorder transition in the membrane lipids, the end points of the transition depending upon the fatty acid composition. The ESR studies for 3 different fatty acid supplements (oleic, elaidic and bromostearic) were confirmed by X-ray diffraction. The characteristic end-point temperatures detected by ESR were the end-point temperatures of a broad order-to-disorder transition of the cytoplasmic membrane lipids. Patterson functions calculated from lamellar X-ray diffraction from partially oriented cytoplasmic membranes indicated a decrease in average membrane thickness upon fatty acid chain melting.