RESOLUTION OF PHOSPHOLIPID MOLECULAR-SPECIES BY P-31 NMR

Phosphorus-31 NMR chemical shifts of phospholipids (PLs) solubilized i n bile salts were studied with respect to variations in the structure of the acyl substituents. The presence of double bonds in the acyl cha ins of phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosph atidylglycerol (PG), and phosphatidic acid (PA) induced small but cons istent up-field shifts relative to the corresponding disaturated acyl PL signals. The magnitudes of the unsaturation-related upfield shifts were approximately twice as large in sodium cholate as in sodium deoxy cholate. Chemical shift separations of PC, PE, and PG dipalmitoyl-diol eoyl species pairs increased slightly at lower temperatures. Resolutio n of the PC species pair was maximized and nearly independent of chola te-to-PL ratio at values greater than about 100 in 2% cholate. Only th e PA species resolution varied significantly over the pH range 6.5 to 9.5, in the vicinity of its pK2. Shift differences for a homologous se ries of disaturated acyl PCs showed a logarithmic dependence on chain length. Spectra for a variety of PC standards were used to interpret t he composite PC signals from egg yolk extract, soybean extract and who le human amniotic fluid. The P-31 NMR analyses were consistent with pu blished chromatographic studies. Interpretation of composite PL signal s in the cholate system is simplified for mixtures having restricted a cyl chain length and degree of unsaturation.