Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0027960 (mole)
 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effects of cholesterol on the dynamics and the structural properties of two different spin probes, the sterol type CSL and the phospholipid type 16-PC, in POPC/cholesterol oriented multilayer model membranes were examined. Our results are consistent with a nonideal solution containing cholesterol-rich clusters created by the self association of cholesterol in POPC model membranes. The lateral diffusion coefficient D of the spin probes was measured over the temperature range of 15 to 60 degrees C and over the concentration range of 0 to 30 mol% of cholesterol in the model membrane by the electron spin resonance (ESR) imaging method. The rotational diffusion coefficients (including R perpendicular) and the order parameter S were determined utilizing a nonlinear least square ESR spectral simulation method. D, R perpendicular and S of CSL deviate considerably from linear dependence on mole percent cholesterol. The D of CSL was decreased by a factor of four at 15 degrees C and a factor of two at 60 degrees C for concentrations of cholesterol over 10 mol %, whereas those of 16-PC were hardly affected. Cholesterol decreased R perpendicular by a factor of 10 at 30 mol % of cholesterol, but it increased slightly that of 16-PC. A significant increase of S for CSL due to the presence of cholesterol was observed. It is shown how the difference in variation of S for CSL vs. 16-PC with composition may be interpreted in terms of their respective activity coefficients, and how a single universal linear relation is obtained for the S of both probes in terms of a scaled temperature. Simple but general correlations of D and of R perpendicular with S were also found, which aid in the interpretation of these diffusion coefficients.
 ...
PMID:Dynamic imaging of lateral diffusion by electron spin resonance and study of rotational dynamics in model membranes. Effect of cholesterol. 253 10

It is shown that good estimates of the activity of cholesterol in phosphatidylcholine-cholesterol mixed model membranes are obtained by examining the orientational order parameter S of cholestane spin probe (CSL) that is obtained from electron spin resonance by spectral simulation. By introducing thermodynamic stability conditions of liquid mixtures, the variation of activity (or S) as a function of cholesterol mole fraction is utilized to predict the concentration at which the phase separation occurs. These results for DMPC and cholesterol binary mixtures agree very well with those of Tempo-partitioning experiments. The comparison of activity coefficients and the phase boundary in DMPC/cholesterol mixtures with those of POPC/cholesterol mixtures suggests that acyl chain unsaturation leads to poorer mixing of cholesterol in phosphatidylcholine model membranes at higher temperatures (i.e., greater than 35 degrees C). In ternary solutions of DMPC, POPC, and cholesterol, it is found that cholesterol shows less deviation from ideality than in either of the two binary mixtures, and this implies that the phase separation occurs at higher cholesterol concentration than in either of the two binary mixtures. The present analysis suggests that there may not be a critical point in DMPC/cholesterol mixtures, even though phase separation does occur.
 ...
PMID:Thermodynamics of phosphatidylcholine-cholesterol mixed model membranes in the liquid crystalline state studied by the orientational order parameter. 255 33

A detailed electron spin resonance (ESR) study of mixtures of 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) and phosphatidylserine (POPS) in oriented multilayers in the liquid crystalline phase is reported with the purpose of characterizing the effects of headgroup mixing on the structural and dynamical properties of the acyl chains. These studies were performed over a range of blends of POPC and POPS and temperatures, utilizing the spin-labeled lipids 16-phosphatidylcholine and 5-phosphatidylcholine as well as cholestane (CSL). The ESR spectra were analyzed by nonlinear least-squares fitting using detailed spectral simulations. Whereas CSL shows almost no variation in ordering and rotational dynamics versus mole fraction POPS, (i.e. XPS), and 5-PC shows small effects, the weakly ordered end-chain labeled 16-PC shows large relative effects, such that the orientational order parameter, S is at a minimum for XPS = 0.5 where it is about one-third the value observed for XPS = 0 and 1. This is directly reflected in the ESR spectrum as a substantial variation in the hyperfine splitting with XPS. The least-squares analysis also shows a reduction in rotational diffusion coefficient, R perpendicular by a fractor of 2 for XPS = 0.5 and permits the estimation of S2, the ordering parameter representing deviations from cylindrically symmetric alignment. These results are contrasted with 2H NMR studies which were insensitive to effects of mixing headgroups on the acyl chains. The ESR results are consistent with a somewhat increased disorder in the end-chain region as well as a small amount of chain tilting upon mixing POPC and POPS. They demonstrate the high sensitivity of ESR to subtle effects in chain ordering and dynamics.
 ...
PMID:An electron spin resonance study of interactions between phosphatidylcholine and phosphatidylserine in oriented membranes. 806 Dec