Deuterium magnetic resonance study of cholesteryl esters in membranes

Abstract

The ternary systems EYL:H2O (50:50 wt %) containing 1 and 5 mol % cholesteryl palmitate-d31 or 1 and 5 mol % cholesteryl palmitate-16,16,16,16-d3 have been studied. Cholesteryl palmitate-d31 gave a unique deuterium magnetic resonance spectrum corresponding to a homogeneous (delta vQ = 3 and 12 kHz) and a solid phase (deltaVQ = 38 and 118 kHz). From the characteristic spectra and spin-lattice relaxation times, a procedure for calculating the amount of each phase present in the ternary mixture is given resulting in a maximum value of homogeneously dissolved cholesteryl palmitate of 0.2 +/- 0.1 mol % and a solid fraction above 0.2 mol %. The most probable order parameter for the (-CD2)n portion of the homogeneous fraction of cholesteryl palmitate-d31 was determined from the quadrupolar splittings to be S = 0.1 which is less than one-half that of the order parameter found for the lecithin chains. Possible explanations for the diminution of the order parameter for cholesteryl ester in bilayers are discussed.

Sterols and membrane dynamics

“…The C16 fatty acid chain folds back into the bilayer hydrophobic interior [22] with the ester adopting a "horseshoe" conformation. The ester linkage is located near the bilayer interface.…”

Deuterium and phosphorus-31 nuclear magnetic resonance of cholesteryl palmitate in dipalmitoylphosphatidylcholine model membranes

“…multilamellar liposomes prepared from the same phospholipid (28) and the same situation has also been encountered for the egg phosphatidylcholineICP system (5,6). The apparent increase in ester solubility upon going from liposomes to small vesicles may simply reflect sonication forcing an excess amount of cholesteryl ester into the bilayer, so that the final sample represents a supersaturated system.…”

“…In our initial study (1) we by sonication of aqueous dispersions to form highly utilized 31P nmr spectroscopy and found that curved unilamellar vesicles, ester intercalation incholesteryl palmitate (CP) increased the permea-creases substantially, reaching as high as 5 mol% bility of model membranes to ions, whereas (6) while the ester chains appear more disordered cholesteryl linoleate did not. The behavior of the compared to CP in multilamellar liposomes (5). saturated ester CP in egg phosphatidylcholine…”

“…The present study is an attempt to determine the bilayer systems was studied by epr of spin-labeled behavior of saturated cholesteryl ester in a highly CP in multilayers (2,3), as well as 13C nmr differ-curved bilayer composed of the completely satuence spectroscopy (4) and ZH nmr (using CP selec-rated phospholipid, dipalmitoylphosphatidyltively deuterated in the acyl chain) (5,6). chloline, both in the presence and absence of The epr studies indicated that only a small frac-cholesterol (20 mol%).…”

“…When nmr-lanthanide shift reagent technique was emselectively deuterated CP in an egg phosphatidyl-ployed (8). Addition of the shift reagent to a sonicholine multilamellar liposome system was studied cated dispersion separates the 31P resonances from using ZH nmr spectroscopy, a smaller fraction of the inside and outside surfaces of the vesicles, and, added ester (-0.2 mol%) was found to intercalate from the relative intensity of the signals, an average between egg phosphatidylcholine molecules (5). If vesicle radius may be estimated.…”