2H nuclear magnetic resonance order parameter profiles suggest a change of molecular shape for phosphatidylcholines containing a polyunsaturated acyl chain

• Published in: Biophysical journal Vol. 68; no. 6; pp. 2396 - 2403
• Main Authors: Holte, L.L., Peter, S.A., Sinnwell, T.M., Gawrisch, K.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01-06-1995; The Biophysical Society
• Subjects: Deuterium; Fatty Acids, Unsaturated; Lipid Bilayers; Magnetic Resonance Spectroscopy - methods; Models, Molecular; Molecular Conformation; Phosphatidylcholines - chemistry; Structure-Activity Relationship; Thermodynamics
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1016/S0006-3495(95)80422-4

Solid-state 2H nuclear magnetic resonance spectroscopy was used to determine the orientational order parameter profiles for a series of phosphatidylcholines with perdeuterated stearic acid, 18:0d35, in position sn-1 and 18:1 omega 9, 18:2 omega 6, 18:3 omega 3, 20:4 omega 6, 20:5 omega 3, or 22:6 omega 3 in position sn-2. The main phase transition temperatures were derived from a first moment analysis, and order parameter profiles of sn-1 chains were calculated from dePaked nuclear magnetic resonance powder patterns. Comparison of the profiles at 37 degrees C showed that unsaturation causes an inhomogenous disordering along the sn-1 chain. Increasing sn-2 chain unsaturation from one to six double bonds resulted in a 1.6-kHz decrease in quadrupolar splittings of the sn-1 chain in the upper half of the chain (or plateau region) and maximum splitting difference of 4.4 kHz at methylene carbon 14. The change in chain order corresponds to a decrease in the 18:0 chain length of 0.4 +/- 0.2 A with 18:2 omega 6 versus 18:1 omega 9 in position sn-2. Fatty acids containing three or more double bonds in sn-2 showed a decrease in sn-1 chain length of 0.7 +/- 0.2 A compared with 18:1 omega 9. The chain length of all lipids decreased with increasing temperature. Highly unsaturated phosphatidylcholines (three or more double bonds in sn-2) had shorter sn-1 chains, but the chain length was somewhat less sensitive to temperature.