Bilayers of arachidonic acid containing phospholipids studied by 2H and 31P NMR spectroscopy

The configurational properties and dynamics of the arachidonic acyl chains of phospholipid bilayers have been investigated for the first time by solid-state 2H NMR techniques, with the goal of achieving a better understanding of the biological roles of polyunsaturated phospholipids. Vinyl perdeuterated arachidonic acid (20:4Δ5,8,11,14-d8) was prepared from eicosatetraynoic acid (ETYA) and was esterified with 1-palmitoyl-sn-glycero-3-phosphocholine to yield 1-palmitoyl-2-vinylperdeuterioarachidonoyl-sn-glycero-3-phosphocholine [(16:0)(20:4-d8)PC]. 31P NMR spectra of aqueous dispersions of (16:0)(20:4-d8)PC as well as 1-perdeuteriopalmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine [(per-2H-16:0)(20:4)PC] were characteristic of the lamellar liquid-crystalline state. The dispersions had similar 31P chemical shift anisotropies, with little apparent motional averaging of the lineshapes due to macroscopic reorientation of liposomes or lateral diffusion of phospholipids about their curved surfaces. Comparison to other phosphatidylcholines indicated that both samples comprised the fully hydrated Lalpha phase plus excess water. Simple models for interpretation of the findings are briefly mentioned and discussed. The results indicate clearly that the structural and dynamic properties of polyunsaturated acyl chains differ from those of saturated and monounsaturated chains in phospholipid bilayers