Electron spin resonance study of the interaction of alpha-tocopherol with phospholipid model membranes.
The effect of up to 20 mol% incorporation of alpha-tocopherol on acyl chain order and dynamics in liquid crystalline phosphatidylcholine (PC) membranes was studied as a function of acyl chain unsaturation by electron spin resonance (ESR) of 5-, 7-, 12- and 16-doxyl spin labelled stearic acids intercalated into the membrane. Order parameters S in the upper portion of the chain (positions 5 and 7) and correlation times tau C in the lower portion (positions 12 and 16) determined from the ESR spectra indicate that in general alpha-tocopherol restricts acyl chain motion within the membrane. The magnitude of the increases in order appears to be dependent upon phospholipid molecular area, being the greatest (up to 15%) in saturated dimyristoylphosphatidylcholine (14:0-14:0 PC) which possesses a relatively small area per molecule as opposed to much smaller increases (less than 3%) in unsaturated PC membranes of larger molecular area. This behavior is interpreted as incompatible with the hypothesis of Lucy and coworkers (A.T. Diplock and J.A. Lucy (1973) FEBS Lett. 29, 205-210), who proposed that membranes are structurally stabilized by interactions between the phytyl side chain of alpha-tocopherol and the polyunsaturated chains of phospholipids.
Wassall
S R
SR
Department of Physics, Indiana University-Purdue University, Indianapolis 46205.
Wang
L
L
McCabe
R C
RC
Ehringer
W D
WD
Stillwell
W
W
D004578:Electron Spin Resonance Spectroscopy; D008567:Membranes, Artificial; D008954:Models, Biological; D015394:Molecular Structure; D010743:Phospholipids / Q000737:chemistry*; D014810:Vitamin E / Q000737:chemistry*
D008567:Membranes, Artificial; D010743:Phospholipids; D014810:Vitamin E