Metabolism of Membrane Phospholipids and Its Relation to a Novel Class of Oligosaccharides in Escherichia coli

Abstract

Phosphatidylethanolamine is metabolically stable in exponentially growing cells of Escherichia coli, whereas phosphatidylglycerol and cardiolipin (diphosphatidylglycerol), labeled by growth in the presence of sn-[2-(3)H]glycero-3-(32)P, lose their radioactivity during subsequent growth on unlabeled medium. We have found that the loss of label from the lipid fraction is accompanied by its appearance in a novel type of cell constituent of E. coli, a closely related group of oligosaccharides, each containing glycerol and phosphoric acid in equimolar proportions, probably derived as intact glycerophosphate units from phosphatidylglycerol and/or cardiolipin. Glucose is the sole detectable sugar. The glycerophosphate-containing oligosaccharides may be fractionated by ion-exchange chromatography into several subfractions, some of which contain succinic acid in ester linkage. Although apparently derived from membrane phospholipids, the newly discovered substances contain no fatty acids, are soluble in water, and are insoluble in organic solvents such as chloroform. They comprise about 0.5-1% of the dry weight of growing cells.