Ripple phases induced by alpha-tocopherol in saturated diacylphosphatidylcholines.
The effect of alpha-tocopherol on the structure and phase behavior of dilauroyl-, dimyristoyl-, dipalmitoyl-, and distearoyl-phosphatidylcholines was examined using X-ray diffraction and freeze-fracture electron microscopic methods. A ripple phase was observed in all of the mixtures at temperatures well below the pretransition temperature of the corresponding pure phospholipid. Freeze-fracture studies indicated that with proportion of alpha-tocopherol less than 5 mol% a ripple phase with large periodicity (50-150 nm) predominated and with about 10 mol% alpha-tocopherol a ripple phase of periodicity about 16 nm was formed. With more than 10 mol% alpha-tocopherol planar bilayers tended to be formed. Partial phase diagrams of mixed aqueous dispersions of saturated phosphatidylcholines and alpha-tocopherol over temperature ranges about the gel to liquid-crystal phase boundary have been constructed. Alpha-tocopherol-enriched domains form ripple phases that coexist with regions of lamellar gel phase of the pure phospholipid in mixtures containing less than 10 mol% alpha-tocopherol. The presence of increasing amounts of alpha-tocopherol in the phospholipid causes an increase in the proportion of ripple phase at the expense of pure phospholipid bilayer indicating that the alpha-tocopherol-enriched domains might possess a defined stoichiometry of the two constituents.
Wang
X
X
Division of Life Sciences, King's College London, United Kingdom.
Semmler
K
K
Richter
W
W
Quinn
P J
PJ
D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry / Q000378:metabolism; D005614:Freeze Fracturing; D008854:Microscopy, Electron; D010713:Phosphatidylcholines / Q000737:chemistry / Q000378:metabolism*; D017356:Synchrotrons; D013696:Temperature; D014810:Vitamin E / Q000737:chemistry / Q000378:metabolism*; D014961:X-Ray Diffraction
D010713:Phosphatidylcholines; D014810:Vitamin E; C015153:1,2-dilauroylphosphatidylcholine; C010942:1,2-distearoyllecithin; D004134:Dimyristoylphosphatidylcholine