Hydration and molecular motions in synthetic phytanyl-chained glycolipid vesicle membranes.
Proton permeation rates across membranes of a synthetic branch-chained glycolipid, 1,3-di-O-phytanyl-2-O-(beta-D-maltotriosyl)glycerol (Mal3(Phyt)2) as well as a branch-chained phospholipid, diphytanoylphosphatidylcholine (DPhPC) were lower than those of straight-chained lipids such as egg yolk phosphatidylcholine (EPC) by a factor of approximately 4 at pH 7.0 and 25 degrees C. To examine whether degrees of water penetration and molecular motions in Mal3(Phyt)2 membranes can account for the lower permeability, nanosecond time-resolved fluorescence spectroscopy was applied to various membranes of branch-chained lipids (Mal3(Phyt)2, DPhPC, and a tetraether lipid from an extremely thermoacidophilic archaeon Thermoplasma acidophilum), as well as straight-chained lipids (EPC, 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC), and digalactosyldiacylglycerol (DGDG)) using several fluorescent lipids. Degrees of hydration of glycolipids, Mal3(Phyt)2, and DGDG were lower than those of phospholipids, EPC, POPC, and DPhPC at the membrane-water interfaces. DPhPC showed the highest hydration among the lipids examined. Meanwhile, rotational and lateral diffusive motions of the fluorescent phospholipid in branch-chained lipid membranes were more restricted than those in straight-chained ones. The results suggest that the restricted motion of chain segments rather than the lower hydration accounts for the lower proton permeability of branch-chained lipid membranes.
Baba
T
T
Nanotechnology Research Institute, Tsukuba, Ibaraki, Japan. t-baba@aist.go.jp
Minamikawa
H
H
Hato
M
M
Handa
T
T
D004058:Diffusion; D004530:Egg Yolk / Q000737:chemistry; D006017:Glycolipids / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008055:Lipids / Q000737:chemistry; D008956:Models, Chemical; D010713:Phosphatidylcholines / Q000737:chemistry*; D011522:Protons; D013050:Spectrometry, Fluorescence; D013696:Temperature; D013997:Time Factors; D014867:Water / Q000737:chemistry / Q000378:metabolism*
D006017:Glycolipids; D008055:Lipids; D010713:Phosphatidylcholines; D011522:Protons; D014867:Water; C021016:1,2-diphytanoylphosphatidylcholine