GLYCEROL BACKBONE CONFORMATION IN PHOSPHATIDYLCHOLINES IS PRIMARILY DETERMINED BY THE INTRAMOLECULAR STACKING OF THE VICINALLY ARRANGED ACYL CHAINS

To analyse the effect of the altered glycerol backbone structure on th e glycerophospholipid conformation, we have replaced the glycerol moie ty by the rac-1,2,4-butanetriol residue in 1,2-diacyl-sn-glycero-3-pho sphocholines (PC), and then analysed the resulting anoyloxy-rac-but-4- yl-[2-(trimethylammonium)ethyl] phosphates (1,2-bPC) and anoyloxy-rac- but-4-yl-[2-(trimethylammonium)ethyl] phosphates (1,3-bPC) by high-res olution H-1- and C-13-NMR spectroscopy in both CDCl3 and D2O, The pref erred conformation about the C1-C2 glycerol bond in PC was almost comp letely preserved in 1,2-bPC, but it was completely random in case of 1 ,3-bPC. Out of the three C-C bonds present in the butanetriol backbone of 1,3-bPC, only the C2-C3 bond experienced a restricted rotation. Ho wever, the conformational preference about this bond was virtually sim ilar to that observed for the C1-C2 bond in PC. These results clearly demonstrate that the preferred conformation of the glycerol backbone i s determined primarily by the intramolecular acyl chain stacking which essentially requires a vicinal arrangement of the acyl chains in glyc erophospholipids.