Effects of membrane-lipid composition on nascent protein translocation induced by heat and ethanol in Escherichia coli

1. 1.|In fatty acid supplemented E. coli auxotrophs the degree of saturation in acyl chains 18 carbons long did not influence the translocation of protein to the outer membrane under hyperthermal stress. However, in cells grown in medium supplemented with 20-carbon fatty acids the degree of saturation markedly affected protein translocation and acute exposure of cells to 6% (v/v) ethanol mimicked the effects of hyperthermic treatment. 2. 2.| 31PNMR studies revealed that whole membranes exhibited lamellar properties at 25°C but at growth temperature (39°C) and above they exhibited a mainly isotropic nature irrespective of fatty acid supplement. At temperatures greater than 40°C, a new isotropic component ( ca 20 ppm downfield) was observed. This isotropic component does not appear to arise from any typical phosphorus metabolite or lipid phase. 3. 3.|The role of lipid composition in protein translocation induced by ethanol and heat stress are discussed and a hypothesis for heat shock activation is presented.