Microimmiscibility and three-dimensional dynamic structures of phosphatidylcholine-cholesterol membranes: translational diffusion of a copper complex in the membrane
- 28 August 1990
- journal article
- research article
- Published by American Chemical Society (ACS) in Biochemistry
- Vol. 29 (34) , 7936-7945
- https://doi.org/10.1021/bi00486a023
Abstract
Saturated and unsaturated phosphatidylcholine (PC)-cholesterol membranes have been studied, with a special attention paid to fluid-phase immiscibility in cis-unsaturated phosphatidylcholine (PC)-cholesterol membranes as previously proposed and to the three-dimensional structure of the membrane. The investigation was carried out with dual probes: a membrane-soluble, square-planar copper complex, (3-ethoxy-2-oxobutyraldehyde bis(N4,N4-dimethylthiosemicarbazonato))copper(II) (CuKTSM2), and one of several nitroxide radical lipid-type spin-labels. Biomolecular collison rates between metal ion and spin-label were determined by measuring the nitroxide spin-lattice relaxation times (T1''s) in the presence and absence of CuKTSM2 by use of saturation-recovery ESR techniques, and from these measured rates, translational diffusion coefficients of CuKTSM2 were estimated. Profiles of the collision rate across the membrane bilayer were obtained with Tempocholine phosphatidic acid ester, 5-doxylstearic acid, 16-doxylstearic acid, and cholesterol-type spin-labels as a function of cholesterol mole fraction, length and unsaturation of acyl chains, and temperature. In the liquid-crystalline phase of saturated PC membranes, incorporation of cholesterol decreases the collision rate at all depths in the membrane, and the effect of cholesterol is smallest in the middle of the bilayer. In trans-unsaturated PC membranes, a cholesterol-induced decrease of the collision rate was also observed, except in the head-group regions. In cis-unsaturated PC membranes, virtually no effect of cholesterol was observed on the collision rate, either with phospholipid-type spin-labels or with cholesterol-type spin-labels. This result is in clear contrast with our previous observaiton, in which the effect of cholesterol in cis-unsaturated PC membranes is small on the alkyl-chain motion of phospholipid-type spin-labels but large on the wobbling rotational diffusion of cholesterol-type spin-labels [Pasenkiewicz-Gierula, M., Subczynski, W. K., and Kusumi, A. (1990) Biochemistry 29, 4059-4069]. A model is proposed to explain these results in which the fluid-phase immiscibility is prevalent in cis-unsaturated PC-cholesterol membranes, but where cholesterol-rich (cholesterol oligomeric) domains are small (several lipids) and/or of short lifetime (10-9 s to < 10-7 s). It is suggested that this microimmiscibility arises from the structural nonconformability between the rigid cholesterol ring structure and the rigid bend at the cis double bonds in PC alkyl chains. Our results also suggest that free volume is created in the central part of the bilayer by intercalation of cholesterol in the membrane due to the short bulky tetracyclic ring of cholesterol, which is enhanced by the mismatch in the hydrophobic length due to the longer PC acyl chains (than cholesterol) and the structural nonconformability between cholesterol and cis-unsaturated PC.Keywords
This publication has 41 references indexed in Scilit:
- The Role of Cholesterol in Regulating Membrane FluidityPublished by Elsevier ,1985
- The structure of lipid bilayers and the effects of general anaestheticsJournal of Molecular Biology, 1979
- Lipid lateral diffusion by pulsed nuclear magnetic resonanceBiochemistry, 1979
- The organisation of cholesterol and ergosterol in lipid bilayers based on studies using non-perturbing fluorescent sterol probesBiochimica et Biophysica Acta (BBA) - Biomembranes, 1979
- Lateral diffusion in binary mixtures of cholesterol and phosphatidylcholines.Proceedings of the National Academy of Sciences, 1979
- The effect of cholesterol on the structure of phosphatidylcholine bilayersBiochimica et Biophysica Acta (BBA) - Biomembranes, 1978
- Models for lipid organization in cholesterol‐phospholipid bilayers including cholesterol dimer formationLipids, 1978
- Spectroscopic studies of specifically deuterium labeled membrane systems. Nuclear magnetic resonance investigation of the effects of cholesterol in model systemsBiochemistry, 1978
- An ESR study of the anchoring of spin-labeled stearic acid in lecithin multilayersChemistry and Physics of Lipids, 1976
- A deuterium nuclear magnetic resonance study of the condensing effect of cholesterol on egg phosphatidylcholine bilayer membranes. I. Perdeuterated fatty acid probesChemistry and Physics of Lipids, 1976