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PubMed1976

An ESR study of the hydration steps of lecithin multilayers.

A spin-labeled stearic acid and other spin-labeled molecules have been used for an ESR study of the hydration process of the egg lecithin lamellar phase for water concentrations, CW greater than 10%. Two hydration steps are found for CW approximately 20% and CW congruent to 30%, in good agreement with results of the literature. To explain discontinuities in the behavior of three spin-labeled molecules at CW congruent to 20%, a conformational change of the phosphatidylcholine polar head and a phase transition in the polar interface are proposed.

Binding Sites↗
PubMed1977

Ultracentrifugation of hydrated egg lecithin in benzene solution.

Estimations of molecular weights from sedimentation equilibrium experiments indicate that the degree of aggregation of egg lecithin in benzene solutions increases with increasing addition of water. The molecular weight rises monotopically from about 14,000 in the anhydrous state to about 57,000 at a water/lecithin ratio of 0.31. Sedimentation coefficients were shown to behave in the same manner. Frictional coefficients obtained from the combined results fail to indicate definite differences in asymmetry; however, they seem to indicate that the aggregates in all stages are compact in shape.

Benzene↗
PubMed1985

Lecithin:cholesterol acyltransferase regulation. II. Effect of fluidity of egg phosphatidylcholine vesicles.

The regulation of human plasma lecithin:cholesterol acyltransferase (LCAT) by changes in bilayer fluidity of substrate egg phosphatidylcholine (egg PC) unilamellar vesicles was investigated using pyrene excimer fluorescence to measure fluidity. Fluidity was decreased by adding up to 20% cholesterol or increased by adding up to 10% egg 2-lysophosphatidylcholine (lysoPC). The fluidizing effect of lysoPC was suppressed by the addition of cholesterol. LCAT activity with 10% cholesterol vesicles was decreased by adding 5% lysoPC, yet activity with 5% cholesterol vesicles was unaffected by adding 5% lysoPC. This difference may be explained by a balance between the known LCAT inhibitory effect of lysoPC and its ability to increase bilayer fluidity and thereby increase LCAT activity. LCAT esterification of up to 37% of vesicle cholesterol failed to alter the lysoPC/cholesterol balance sufficiently to influence activity in this system. The findings of our studies are in keeping with modulation of LCAT activity by bilayer fluidity, but fluidity changes caused by enzyme action are not sufficient to regulate that activity.

Egg Yolk↗
PubMed1986

Synthesis, calorimetry, and X-ray diffraction of lecithins containing branched fatty acid chains.

Lecithins with branched fatty acid chains were synthesized and characterized by differential scanning calorimetry and X-ray diffraction. The influence of three chemical alterations on the phase transition parameters were investigated: length of the branches in 2-position of the acyl chains, position of the branches in the acyl chains, and position of the branched fatty acid chains in the glycerol backbone. The results show that the branched phosphatidylcholines (PCs) have a reduced gel-to-liquid-crystalline phase transition temperature (Tm) compared to the corresponding straight-chain PCs. Depending on both the length of the branches in 2-position of the acyl chains and the position of the branches in the acyl chains, the Tm-values pass through a minimum. The systematic change of the main-transition temperatures Tm is connected with a modified structural polymorphism. If the length of the branches increases three types of polymorphism were observed.

Calorimetry, Differential Scanning↗
PubMed1986

Liposome formation of egg lecithin and its interaction with iodine.

The sonicated dispersion of egg lecithin (phosphatidylcholine) in water forms 1:1 molecular complex with iodine, when its concentration is above 1.6 X 10(-5) M. The thermodynamic and spectrophotometric properties of this complex have been determined. The thermodynamic values are: K (25 degrees C) = 1.6 X 10(3) 1 X mol-1, delta G degrees = -18.4 KJ X mol-1, delta H degrees = -27.4 KJ X mol-1 and delta S degrees = -30.0 J X mol-1 X deg-1. The complex shows two absorption bands: one at 293 nm, which is the charge transfer band and the other at 370 nm, which is the blue shifted visible iodine band at 460 nm in water.

Animals↗
PubMedDate not supplied

Properties of lecithin-dodecaprenol macrovesicular bilayer membranes.

The ionic transport properties, capacitance and breakdown voltage of bilayer macrovesicles made from lecithin, dodecaprenol and their mixtures have been studied. The electrical measurements showed that polyprenol in lipid bilayers increases membrane permeability and elasticity, and decreases membrane thickness. Some physiological implications of these findings are indicated.

Egg Yolk↗
PubMed1990

Solubilization of multilamellar liposomes of egg yolk lecithin by the bile salt sodiumtaurodeoxycholate and the effect of cholesterol--a rapid-ultrafiltration study.

The solubilization of multilamellar egg yolk lecithin liposomes by sodiumtaurodeoxycholate in aqueous phase was studied by ultrafiltration as a function of time, bile salt and cholesterol concentration. The corresponding equilibrium states were analysed. Complete solubilization was achieved at total bile salt/lecithin molar mixing ratios of approximately 5. The minimum ratio to start solubilization was 0.1, corresponding to a free bile salt concentration of only 5% of the critical micelle concentration (CMC). Mean equilibrium constants for the partition of bile salts between non-filterable aggregates and filterable mixed micelles and also the free bile salt concentration were determined. Sodiumtaurodeoxycholate had a higher affinity for small mixed micelles than for lamellar mixed aggregates especially in the presence of cholesterol, which reduces the degree and rate of the solubilization process. A non-homogeneous distribution of bile salts in the lipid phase was detected at low bile salt concentrations.

Bile Acids and Salts↗
PubMed1975

Quantitative studies of lipoprotein-X in familial lecithin: cholesterol acyltransferase deficiency and during cholesterol esterification.

In eight patients with familial lecithin: cholesterol acyltransferase (LCAT) deficiency the plasma concentration of the abnormal lipoprotein LP-X ranged from 43 mg/100 ml to 251 mg/100 ml with a mean of 127 mg/100 ml. This is above the mean level of LP-X found in a group of patients with intrahepatic cholestasis (49 mg/100 ml) and below the mean level found in patients with extrahepatic cholestasis (341 mg/100 ml). Following blood transfusions, an increase in LCAT activity and a decrease in the plasma concentration of LP-X were observed. This decrease was not a simple dilution phenomenon. Quantitation of LP-X during long-term incubation of a whole plasma system demonstrated that LP-X was a source of free cholesterol (FC) in the LCAT reaction. More free cholesterol was derived from LP-X during cholesterol esterification than corresponding to the percentage of the plasma free cholesterol found in the LP-X fraction. The present investigation did not answer the question whether LP-X only was an easily accessible source of free cholesterol for cholesterol esterification or whether LP-X acted directly as a substrate for the LCAT reaction.

Acyltransferases↗
PubMed1975

Lecithin:cholesterol acyltransferase initial fractional rates of esterification in human and rat serum during development.

The initial fractional rates of cholesterol esterification were measured in human cord serum, in a group of apparently healthy "young adults" (mean age +/- S.D. 32 +/- 5 years), in a group of "middle aged" adults (51 +/- 8 years) with normal coronary angiograms and in newborn, 10-, 20-, 45-, 180- and 365-day-old rats. The initial fractional rate of esterification was inversely related to serum cholesterol levels in humans and, with the exception of newborns, also in rats. A theory of lecithin:cholesterol acyltransferase participation in cholesterol metabolism is discussed.

Acyltransferases↗
PubMed1977

[Determination of lecithin-cholesterol acyltransferase. Studies on the precipitation of beta-lipoproteins by dextran sulphate (author's transl)].

Uncertainties in assays of lecithin-cholesterol acyltransferase (LCAT) are generally related to the degree of isotopic equilibrium obtained by rapid exchange of unesterified cholesterol between the different lipoproteins. A new method is presented based on the precipitation of serum beta-lipoprotein with sulfated polysaccharides prior to the LCAT determination. In the absence of Beta-lipoproteins, more than 7 per cent of serum free cholesterol is esterified in the first hour and the reaction rate is linear for about 2 h. LCAT activities with normal serum expressed as cholesterol esterified per microliter mol/1/h are lower than the values reported by others. The reason for this discrepancy is that free cholesterol specific activity in total serum does not reflect the true specific activity of LCAT cholesterol substrate.

Chemical Precipitation↗
PubMed1978

Similar behaviour of lecithin:cholesterol acyltransferase and pseudocholinesterase in liver disease and hyperlipoproteinemia.

Using exogenous substrate for its assay, lecithin:cholesterol acyltransferase (LCAT) was found to be decreased in liver disease and higher than normal in endogenous hypertriglyceridemia. LCAT activity was positively correlated with serum cholesterol and triglyceride. However in the six patients with excessive hypertriglyceridemia (type V), LCAT activity was lower than in type IV hyperlipoproteinemia. LCAT activity was not changed significantly in type II-a hyperlipoproteinemia. A striking parallel was noted between plasma LCAT and serum pseudocholinesterase activity. It suggested that both these liver secretion enzymes might be induced by an accelerated turnover of serum lipids and lipoproteins. Pathogenical implications of these findings are briefly discussed.

Adult↗
PubMed1980

The determination of lecithin:cholesterol acyl transferase in the clinical laboratory: a modified enzymatic procedure.

A very simple and fast method for the determination of lecithin:cholesterol acyltransferase is described. The method is based on the enzymatic determination of free cholesterol in a serum or plasma sample before and after 40 min incubation at 37 degrees C. The proposed procedure is particularly useful for routine application in a clinical laboratory. It works with a coefficient of variation of less than 5%.

Cholesterol↗
PubMed1982

The role of lecithin: cholesterol acyltransferase in high density lipoprotein3/high density lipoprotein2 interconversion.

Serum was incubated in vitro with and without inhibition of lecithin:cholesterol acyltransferase (LCAT, EC 2.3.1.43). High density lipoprotein2 (HDL2) and high density lipoprotein3 (HDL3) were separated by zonal ultracentrifugation and analysed for lipid and apoprotein contents. The incubation of fresh sera resulted in a time-dependent decrease in HDL3 and an increase in HDL2. At the end of 24 h incubation HDL3 disappeared completely and the HDL2 peak had reached its maximum. The newly formed HDL2 was relatively enriched in total protein (apoprotein A-I, C-apoproteins) and cholesteryl esters, and depleted in phosphatidylcholine. Its migration in polyacrylamide gel electrophoresis was identical with HDL2 contained in fresh serum or HDL2 isolated from serum by zonal ultracentrifugation. The generated HDL2 particles exhibited the same electron microscopical characteristics as reference HDL2 samples prior to incubation. Addition of Ellman's reagent to the incubation mixture or heat inactivation of the samples prior to incubation resulted in a complete inhibition of HDL3/HDL2 interconversion, whereas addition of 1 mol/l NaCl had no detectable influence. There was also a substantial increase in HDL2 when VLDL-deficient serum was incubated at 37 degrees C. Similarly, in fresh serum from a patient affected with familial lipoprotein lipase deficiency, HDL3 was completely converted to HDL2. Our experiments demonstrate that LCAT promotes HDL3/HDL2 interconversion in native serum irrespective of the presence or absence of triglyceride-rich lipoproteins and lipoprotein lipase.

Adult↗
PubMed1982

Plasma lecithin-cholesterol acyltransferase activities in uraemic patients.

Plasma lecithin-cholesterol acyltransferase (LCAT) activity was measured in 43 haemodialysis and 15 peritoneal dialysis (CAPD) patients. LCAT activities in both groups of patients were significantly lower than those of normal subjects and did not correlate with any of the other biochemical parameters studied. The effect of intravenous administration of 100 U/kg of heparin on LCAT activity was examined in 21 haemodialysis patients and 19 normal subjects. Heparin inhibited LCAT activity by increasing plasma free fatty acid concentrations. LCAT remained inhibited throughout a dialysis session and returned towards pre-dialysis levels an hour after haemodialysis was discontinued. The cause of the low LCAT activities in the patients was not certain, but did not appear to be due to the presence of inhibitors in the uraemic plasma. The significance of these findings is discussed.

Adult↗
PubMed1983

Plasma lecithin:cholesterol acyltransferase -- reference values and effects of xenobiotics.

Plasma lecithin:cholesterol acyltransferase (LCAT) has been measured by an enzymatic method. We did not observe any significant sex variations, but age variations were found. In females, LCAT activities are stable up to 40 years (60 mumol . 1.1 . h-1 at the 50th centile). Also, from 50 years the median increased progressively to 76 mumol . 1-1 . h-1. In males, the activity increased from 52 to 71 mumol . 1-1 . h-1 at the 50th centile in two age groups (15-20 years and 50 years). The effect of some xenobiotics on LCAT activity was studied. We observed an increase in activity of 33% in males when the daily alcoholic beverage consumption ranged from 0 to more than 0.5 litre of wine or beer. LCAT activity increased in children who were treated with hypolipidemic drugs (fenofibrate, Lipanthyl). In boys, the mean enzyme activity increased to 35% (p less than 0.05). The increase was greater in girls (75%, p less than 0.01). Treatment with anticonvulsant drugs gave a decrease in LCAT activity of 32-46%.

Adolescent↗
PubMed1983

Lecithin: cholesterol acyltransferase in Down's syndrome.

Based on earlier reports indicating that Down's syndrome may represent an atheroma-free human model, two groups of institutionalized subjects were compared with respect to various parameters of their plasma lipid transport system. One group of subjects was comprised of Down's syndrome subjects and the second, a group of mentally retarded individuals. Parameters measured included plasma cholesterol, triglyceride, HDL-cholesterol, apolipoprotein levels (A-I, B, C-III, and E), lecithin:cholesterol acyltransferase (LCAT) activity, body mass and blood pressure. Statistical analyses indicated no significant differences between the two groups except for the lower fractional rate of cholesterol esterification (% cholesterol esterified per hour, p = 0.0049) in the Down's syndrome subjects. Adjustment for the effects of body mass and age revealed no other significant differences between the two groups except for a lower molar rate of esterification (nmol cholesterol esterified X h-1 X ml-1, p less than 0.0063) in the Down's syndrome subjects. Additional differences between the two groups were revealed by partial correlational analyses of LCAT activity with the measured parameters or ratios of these parameters which suggests that the composition and/or metabolism of lipoproteins may differ between these two groups. Whether the lower LCAT activity and the other differences reflected by the correlational analyses contribute to the decreased incidence of atherosclerotic lesions in Down's syndrome remains to be elucidated.

Adolescent↗
PubMed1988

Lack of association between plasma lecithin: cholesterol acyltransferase concentration and plasma sex hormone concentrations in men.

Plasma lecithin:cholesterol acyltransferase (LCAT) concentration has been shown to be higher in women than in men, suggesting that sex hormones may influence LCAT metabolism. In order to explore this possibility, the associations of plasma LCAT concentration with the concentrations of total, free and protein-bound testosterone, 5 alpha-dihydrotestosterone and oestradiol in plasma, and with total androstenedione concentration in plasma, were examined in 88 men aged 52-67 yr. Total cortisol in plasma was also assayed. No statistically significant correlations were observed between LCAT and androgen or oestrogen concentrations, but a weak positive association was observed between LCAT and plasma cortisol concentration (r = +0.227, p less than 0.05).

Aged↗
PubMed1995

Reactivity of lecithin-cholesterol acyl transferase (LCAT) towards glycated high-density lipoproteins (HDL).

Hyperglycaemia in diabetic patients results in non-enzymatic glycation of plasma proteins, including lipoproteins such as high-density lipoproteins (HDL). We studied the effects of in vitro HDL glycation on the activity of lecithin-cholesterol acyl transferase (LCAT), a key enzyme in HDL plasma metabolism. LCAT was prepared from non-diabetic subjects and HDL by sequential density ultracentrifugation (in the density range of 1.063-1.21 g/ml) from both diabetic and non-diabetic patients. HDL from non-diabetic patients were glycated in vitro by incubating lipoproteins with 100 mmol/l glucose for various times at 37 degrees C with sodium cyanoborohydride as reducing agent. Glycation of HDL protein was quantified by measuring the percentage of derived amino acid residues using the TNBS assay. Kinetic parameters of LCAT were first determined using native HDL from non-diabetic patients and in vitro glycated HDL. With native HDL, Km and Vmax were 51.1 +/- 4.2 mumol/l (n = 8) and 12.9 +/- 2.4 nmol/ml/h (n = 8), respectively. Enzyme reactivity, calculated as the Vmax/Km ratio, was 0.25 +/- 0.04 h-1 (n = 8). In the case of moderate glycation (derived residues < 30%; n = 19) a significant increase in both Km (18.2 +/- 3.4%; mean +/- S.D.) and Vmax (9.3 +/- 2.4%) was observed. In contrast, with a high level of glycation (derived residues > 30%; n = 8), both parameters fell (Km, 25 +/- 6.3%; Vmax, 34.1 +/- 3.3%). In addition, whatever the level of glycation, enzyme reactivity was lower in the presence of in vitro glycated HDL. This decrease in LCAT reactivity was not due to a peroxidative process nor to an alteration of the protein and lipid composition of in vitro glycated HDL. It could, however, be explained by glycation of lysine residues in apolipoprotein A-I, which is the most potent activator of LCAT. In a second series of experiments, native diabetic HDL preparations were used as LCAT substrate. No alteration in Km values was observed, but there was a significant decrease in both Vmax (28%) and enzyme reactivity (32%). This difference in Km and Vmax alterations between native diabetic HDL and in vitro glycated HDL with low levels of glycation might be explained by the impact of physiological modifications, other than glycation, which could differently affect the chemicophysical properties of HDL in diabetic patients.(ABSTRACT TRUNCATED AT 400 WORDS)

Diabetes Mellitus↗