A 2H-NMR study on the glycerol backbone of phospholipids extracted from Escherichia coli grown under high osmotic pressure: evidence for multiconformations of phosphatidylethanolamine.

A glycerol-requiring auxotroph was isolated from mutagenized Escherichia coli K-12 UFAts cells. This auxotroph was used for the specific deuteration of E. coli phospholipids. The cells were grown under high osmotic pressure (in the presence of 2.0% KCl). The membrane had a highly saturated fatty acid composition (76% phosphatidylethanolamine, 20% cardiolipin and 4% phosphatidylglycerol). The deuterium magnetic resonance spectra of coarse liposomes of the extracted phospholipids with perdeuterated glycerol incorporated into them were measured. To obtain well characterized information, phospholipid mixtures reconstituted from the deuterated and nondeuterated components at the same ratios as in the case of the total extract were used. On the analysis of the spectra, the following conclusions were drawn. (1) The whole polar region of cardiolipin is dynamically symmetric and quite rigid in the presence of phosphatidylethanolamine. (2) Although the quadrupole splittings of the deuterons at the C-2 and C-3 positions of the glycerol backbone were similar to each other, those at the C-1 position for phosphatidylethanolamine and cardiolipin are different, even in the same bilayer. (3) Furthermore, each C-1 deuteron of phosphatidylethanolamine gave rise to a doublet, suggesting the presence of two backbone conformations, between which there is slow exchange. (4) The polar head group of phosphatidylethanolamine interacts with cardiolipin and phosphatidylglycerol in different ways, which could be responsible for the different osmotic properties of the vesicles composed of them.