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 (20:4 delta 5,8,11,14-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-phosphocho line [(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 L alpha phase plus excess water. However, the dispersion of (16:0)(20:4-d8)PC yielded relatively narrow powder-type 2H NMR spectra, compared to (per-2H-16:0)(20:4)PC in the liquid-crystalline state. The differences in the 2H NMR powder patterns thus reflect differences in the configurational properties of the polyunsaturated sn-2 arachidonic acyl chain compared to the saturated sn-1 palmitic chain. When the powder-type 2H NMR spectra of the (16:0)(20:4-d8)PC bilayer were dePaked (theta = 0 degrees), they showed three kinds of deuterons upon integration: one with a large splitting (approximately 25-35 kHz), two with intermediate splittings (approximately 10-15 kHz), and the remainder with smaller splittings (approximately 0.3-5 kHz).(ABSTRACT TRUNCATED AT 250 WORDS)