INTERACTIONS OF LYSO 1-PALMITOYLPHOSPHATIDYLCHOLINE WITH PHOSPHOLIPIDS - A C-13 AND P-31 NMR-STUDY

C-13 and P-31 NMR spectroscopy were used to monitor interactions of lyse 1-palmitoylphosphatidylcholine (LPPC) in the interfacial region of egg phosphatidylcholine (PC) bilayers and determine the effect of LPPC on the phospholipid bilayer structure. C-13 NMR spectroscopy of small amounts (0.5-10 mol %) of C-13 carbonyl-enriched LPPC cosonicated with egg PC to form. small unilamellar vesicles (SUVs) revealed separate carbonyl signals for LPPC in the inner and outer leaflets of the vesicles. The ratio of LPPC in the outer leaflet to that in the inner leaflet was greater than or equal to 3/1. Exchange of LPPC between bilayer leaflets (''flip-flop'') was too slow to be measured (t(1/2) >12 h). Albumin added to the external buffer of LPPC/PC vesicles was shown by C-13 NMR to extract LPPC only from the outer leaflet. LPPC was a poor detergent in egg PC multilayers and SUVs. Stable SUVs were prepared by cosonicating egg PC with up to 30 mol % LPPC, and preformed SUVs incorporated up to 40 mol % of LPPC (added as an aqueous solution) without undergoing any morphological changes as evidenced by P-31 NMR spectroscopy. The presence of oleic or palmitic acid did not have observable effects on properties of LPPC in SUVs, such as the localization of the LPPC carbonyl in the interface, and the transbilayer distribution and movement of LPPC. The apparent pK(a) of the fatty acid (FA) carboxyl at the membrane interface (7.7) measured by C-13 NMR was not affected by LPPC, but the FA carboxyl carbon resonance showed linewidth changes near the apparent pK(a) that were dependent on the FA/LPPC ratio. These data suggest weak interactions in the interfacial region between FA and LPPC when both lipids are present at low levels in PC vesicles.