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At least 973 records · Page 54Linked to original sources
PubMed1982

Antioxidant activities of tocopherols on Fe2+-ascorbate-induced lipid peroxidation in lecithin liposomes.

The antioxidant activities of 4 tocopherols, tocol, and a water-soluble model analog of alpha-tocopherol were compared. Egg lecithin liposomes were used and oxidation was catalyzed by Fe2+-ascorbate. The activities decreased in the order alpha greater than beta greater than gamma greater than delta-tocopherol greater than tocol, in agreement with their potencies in vivo. The water-soluble analog was the least effective. Activity depended on the molar ratio of antioxidant to unsaturated lipid, with one molecule each of the alpha-, beta-, gamma-, delta-tocopherol and tocol capable of protecting, respectively, 220, 120, 100, 30 and 20 molecules of polyunsaturated fatty acid. The mechanism of possible antioxidant effect of the compounds used is discussed.

Ascorbic Acid↗
PubMed1986

Spectroscopic investigations of the water pool in lecithin reverse micelles.

The nature of the water pool formed in the reverse micellar system, lecithin/nonpolar solvent/water, has been investigated by means of near infrared, ultraviolet, fluorescence emission and visible spectroscopic techniques. The three nonpolar solvents chosen in this study were benzene, carbon tetrachloride and cyclohexane. Near infrared spectroscopic studies revealed that the amount of water present in the bulk organic phase is negligible at all water concentrations studied in all three solvents. The results of the polarity probe and 8-anilinonaphthalene sulfonic acid (ANSA) fluorescence emission maxima studies indicate that the polarity of the water pool is much lower than that of bulk water. The difference in polarity between the water pool and bulk water decreases with increasing water concentration in benzene and carbon tetrachloride systems. However, in the cyclohexane system, at a water content of 6 moles of water per mole of lecithin, where the system is known to change from isotropic reverse micelle to anisotropic liquid crystalline state, the polarity of the water pool is found to decrease.

Anilino Naphthalenesulfonates↗
PubMed1991

Comparative specificity of plasma lecithin:cholesterol acyltransferase from ten animal species.

The molecular specificities of plasma lecithin:cholesterol acyltransferase (LCAT) from ten animal species have been compared. Using a reassembled high density lipoprotein containing a mixture of phosphatidylcholines, the relative rates of liberation of different species of cholesteryl ester were measured. All but two species of LCAT clustered according to one of three patterns of substrate specificity. The LCAT from six species, including human, did not transfer highly polyunsaturated fatty acyl chains. In addition, human LCAT transesterified saturated fatty acyl chains more effectively than unsaturated fatty acyl chains. We conclude that the structures of the active sites of the enzymes differ, and that this may be related to size constraints that prevent efficient binding of large bulky phosphatidylcholines.

Animals↗
PubMed1994

Effects of site-directed mutagenesis on the serine residues of human lecithin:cholesterol acyltransferase.

Lecithin:cholesterol acyltransferase (LCAT) is a serine protease-type enzyme that esterifies cholesterol in human plasma and is activated by apolipoprotein A-I in high-density lipoproteins. LCAT contains 22 serine residues, including Ser181, which is thought to be part of the catalytic site. In order to determine the importance of these serine residues in LCAT, we prepared six LCAT mutants: LCAT (Ser19-->Ala), LCAT (Ser181-->Gly), LCAT (Ser208-->Ala), LCAT (SEr216-->Ala), LCAT (Ser225-->Ala) and LCAT (Ser383-->Ala). We also replaced the adjacent asparagine residues in two additional mutants, LCAT (Ser19-->Ala, Asn20-->Thr) and LCAT (Ser383-->Ala, Asn384-->Thr), in order to ascertain the effect of the serines on N-glycosylation. The mutant complementary DNA (cDNA) were subcloned into a eukaryotic expression vector (pSG5) and expressed in COS-6 cells. By polymerase chain reaction analysis, LCAT-specific messenger RNA (mRNA) was found in all mutant and wild-type transfectants. Western blot analysis revealed LCAT-specific bands in media and lysates of the transfected cells. With two exceptions, the amounts of LCAT mass secreted by the transfectants were similar to that of the wild type (mean, 90% mass of wild type; range, 34-138%). Except for LCAT (Ser181-->Gly), which was inactive, the specific activities of the remainder of the mutant enzymes were also similar (mean 95% activity of wild type; range, 65-169%). These results indicate that Ser181 is part of the catalytic site and that stereoconservative substitutions for serines have minor effects on the synthesis, secretion and specific activities of human LCAT.

Base Sequence↗
PubMed1992

Decreased lecithin:cholesterol acyltransferase activity in the plasma of hypercholesterolemic pigs.

Lecithin:cholesterol acyltransferase (LCAT) activity levels were determined, as function of plasma total cholesterol (TC) in 13 normocholesterolemic (TC less than 85 mg/dL) and in 28 hypercholesterolemic (TC greater than 98 mg/dL) pigs. The normocholesterolemic group consisted of pigs that carried apo-B allelic genes other than Lpb5 and or Lpb8. The hypercholesterolemic group consisted of Lpb5/x and Lpb5/8 heterozygous and Lpb5/5 homozygous animals. The data reported in this study show that the LCAT activity in the plasma of hypercholesterolemic (HC) pigs (79 +/- 43 units) was significantly lower (p less than 0.0005) compared to the normocholesterolemic controls (175 +/- 45 units). Furthermore, LCAT activity was positively correlated with TC in the normocholesterolemic group (r = +0.54; p less than 0.05), whereas it was negatively correlated with TC in the hypercholesterolemic group (r = -0.73; p less than 0.001). Additional data obtained from incubation experiments suggest that the lower LCAT activity in hypercholesterolemic pigs may be due, at least in part, to inhibition of LCAT activity by components found in the lipoprotein-deficient fractions of the plasma of hypercholesterolemic pigs.

Animals↗
PubMedDate not supplied

Lipid transport in the hypothyroid rat as reflected by the serum concentrations of free fatty acids, lipoproteins, lecithin-cholesterol acyltransferase and lipoprotein lipase activity in adipose tissue.

An experimental model was explored for the study of the effect of thyroid hormone on lipid transport and metabolism in the rat. The development of the hypothyroid state was accompanied by an early decrease in free fatty acids (FFA) followed by an increase in the level of cholesterol and a decrease in triglyceride concentration. Simultaneously, the adipose tissue lipoprotein lipase activity increased while the lecithin-cholesterol acyltransferase was unchanged. The hypothyroid state was also accompanied by a decrease in the concentrations of tryglycerides and cholesterol in very low density lipoproteins (VLDL) while the 2 lipids increased in the low density lipoprotein (LDL) fraction. Administration of triiodothyronine markedly reduced the amount of cholesterol in both the LDL and high density lipoprotein (HDL) fractions. The animal model has been shown to have similarities with findings in human subjects.

Adipose Tissue↗
PubMed1999

Apolipoprotein A-I (R151C)Paris is defective in activation of lecithin: cholesterol acyltransferase but not in initial lipid binding, formation of reconstituted lipoproteins, or promotion of cholesterol efflux.

ApoA-I(R151)Paris is a natural apolipoprotein (apo) A-I variant that is associated with low levels of high-density lipoprotein cholesterol (HDL-cholesterol) and the partial deficiency of lecithin:cholesterol acyl-transferase (LCAT) in the plasma of heterozygous carriers. We compared the abilities of recombinant normal apoA-I and recombinant apoA-I(R151C)Paris to clear an emulsion of dimyristoylphosphatidylcholine (DMPC), to form reconstituted lipoproteins with dipalmitoylphosphatidylcholine (DPPC), to activate LCAT, and to promote efflux of biosynthetic cholesterol from porcine aortic smooth muscle cells (SMCs) or of exogenous cholesterol from lipid-loaded mouse peritoneal macrophages. Recombinant apoA-I(R151C)Paris occurred in monomeric and dimeric forms at a ratio of 60:40. Normal apoA-I and apoA-I(R151C)Paris cleared DMPC emulsions at equal rates. Both isoforms associated completely with DPPC during cholate dialysis. Normal apoA-I formed one single particle with a mean diameter of 9.3 nm, whereas apoA-I(R151)Paris gave rise to three particles with mean diameters of 9.3 nm (containing 74% of apoA-I), 10.6 nm, and 12.1 nm, respectively. Compared to normal apoA-I, apoA-I(R151C)Paris had a reduced LCAT-cofactor activity with a 60% lower Vmax/Km ratio due to a 50% higher affinity constant, Km. During incubations for 10 min and 360 min, normal apoA-I/DPPC complexes and apoA-I(R151C)Paris/DPPC complexes were equally efficient in releasing biosynthetic cholesterol from SMCs. In the lipid-free form, apoA-I(R151C)Paris induced normal hydrolysis of cholesteryl esters and normal cholesterol efflux from lipid-loaded mouse-peritoneal macrophages. In conclusion, in addition to its ability to form homo- and heterodimers, apoA-I(R151C)Paris is characterized by defective LCAT-cofactor activity but by normal lipid binding and cholesterol-efflux-promoting abilities.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2007

The impact of glycation on apolipoprotein A-I structure and its ability to activate lecithin:cholesterol acyltransferase.

AIMS/HYPOTHESIS: Hyperglycaemia, one of the main features of diabetes, results in non-enzymatic glycation of plasma proteins, including apolipoprotein A-I (apoA-I), the most abundant apolipoprotein in HDL. The aim of this study was to determine how glycation affects the structure of apoA-I and its ability to activate lecithin:cholesterol acyltransferase (LCAT), a key enzyme in reverse cholesterol transport. MATERIALS AND METHODS: Discoidal reconstituted HDL (rHDL) containing phosphatidylcholine and apoA-I ([A-I]rHDL) were prepared by the cholate dialysis method and glycated by incubation with methylglyoxal. Glycation of apoA-I was quantified as the reduction in detectable arginine, lysine and tryptophan residues. Methylglyoxal-AGE adduct formation in apoA-I was assessed by immunoblotting. (A-I)rHDL size and surface charge were determined by non-denaturing gradient gel electrophoresis and agarose gel electrophoresis, respectively. The kinetics of the LCAT reaction was investigated by incubating varying concentrations of discoidal (A-I)rHDL with a constant amount of purified enzyme. The conformation of apoA-I was assessed by surface plasmon resonance. RESULTS: Methylglyoxal-mediated modifications of the arginine, lysine and tryptophan residues in lipid-free and lipid-associated apoA-I were time- and concentration-dependent. These modifications altered the conformation of apoA-I in regions critical for LCAT activation and lipid binding. They also decreased (A-I)rHDL size and surface charge. The rate of LCAT-mediated cholesterol esterification in (A-I)rHDL varied according to the level of apoA-I glycation and progressively decreased as the extent of apoA-I glycation increased. CONCLUSIONS/INTERPRETATION: It is concluded that glycation of apoA-I may adversely affect reverse cholesterol transport in subjects with diabetes.

Apolipoprotein A-I↗
PubMed2002

Electrical capacitance of lipid bilayer membranes of hydrogenated egg lecithin at the temperature phase transition.

Electrical capacitance of the planar bilayer lipid membrane (BLM) formed from hydrogenated egg lecithin (HEL) has been studied during many passages through the phase transition temperature. In contrast to the BLM from individual synthetic phospholipids, membranes from HEL did not demonstrate any capacitance change at the phase transition temperature maximum, as measured by differential scanning calorimeter at 52 degrees C. Instead, two temperatures have been discerned by capacitance records: thickening at 42-43 degrees C and thinning at 57-59 degrees C. The first temperature region is close to the transition temperature of dipalmitoyllecithin, whereas the second is close to that of distearoyllecithin, two main components of the HEL. It was suggested that capacitance measurements were able to reveal a phase separation in the BLM from HEL which was not detected by differential scanning calorimetry. The phase transition of the BLM from the liquid crystal state to the gel state is followed by thickening of the bilayer structure, partly due to a gauche- trans transition of lipid molecules but mainly due to redistribution of the solvent n-decane.

Animals↗
PubMed2005

High yield of long-chain polyunsaturated fatty acids by labyrinthulids on soybean lecithin-dispersed agar medium.

The aim of the present research was to provide an effective long-chain polyunsaturated fatty acid (LCPUFA) production by labyrinthulids using soybean lecithin (SBL). Use of SBL-dispersed agar medium resulted in higher LCPUFA production than soybean oil. Among the components of SBL, phosphatidylinositol (PI) and triacylglycerol (TG) were revealed to be essential factors for high growth of labyrinthulids. PI was effective for surface growth, and TG was effective for three-dimensional growth. The presence of some elements like carotenoids in SBL and the smaller droplet size of dispersed SBL were also attributed to be factors for the higher LCPUFA productivity on SBL medium. LCPUFA productivity and the volume of the oval form of the cells increased with increasing SBL concentration up to 40 g/l. Under optimum conditions, LCPUFA production of the L25 strain, isolated from Ogasawara Island in Japan, reached 2.91 g/l after 21 days.

Agar↗
PubMed1975

Transversal and longitudinal lecithin-sphingomyelin ratios in amniotic and lung fluids of fetal lambs.

Lecithin-sphingomyelin (L/S) ratios were measured in both amniotic and in lung fluids of fetal lambs. Around Day 130 of fetal age sudden increase of L/S ratio appeared in lung fluid. The amniotic L/S ratio increased only slowly as a consequence of which false negative values were obtained. A respiratory distress syndrome is to be expected when the lung fluid shows a L/S ratio less than 2. The L/S ratio of lung fluid is preferable to amniotic L/S ratio. In comparison with those of amniotic fluid the L/S ratios of lung fluid were significantly higher. Lung fluid secretion was measured daily. Large differences were seen among the lambs. Two days before delivery a striking decrease in the quantity of lung fluid production was noticed in all aminals.

Amniotic Fluid↗
PubMed1975

Changes in amniotic fluid lecithin-sphingomyelin ratio following maternal dexamethasone administration.

The effect of dexamethasone on amniotic fluid lecithin-sphingomyelin (L/S) ratio was measured in 15 fetuses of 34 weeks or less of gestation. Six of the patients presented with premature rupture of the membranes. A rise in the L/S ratio is mature levels (two or more) was observed 24 hours to 11 days after the start of treatment in 12 patients. In 2 patients (one second twin and one anencephalic fetus), no rise in L/S ratio occurred. Of 12 cases whch ended in premature delivery (29 to 35 weeks) only one infant, a second twin delivered at the thirtieth week with a posttreatment L/S ration o1.4 weighing 1,240 grams, developed severe respiratory distress syndrome and died. Tt is suggested that dexamethasome accelerates fetal lung maturation by increasing surfactant synthesis or release, and this may be achieved as early as the twenty-eighth week of pregnancy.

Amniotic Fluid↗
PubMed1987

A continuous fluorescence assay for lecithin cholesterol acyltransferase.

A continuous fluorescence assay was adapted to the measurement of the phospholipase reaction of lecithin cholesterol acyltransferase (LCAT). The fluorescent phospholipid 1-acyl-2-(N-4-nitrobenzo-2-oxa-1,3-diazole)aminocaproyl phosphatidylcholine (C6-NBD-PC) in micelle form reacted with LCAT to yield NBD-caproic acid, resulting in up to 5-fold increases in fluorescence in 30 min. The reaction rates were optimal in mixtures containing 0.1 M NaCl and 4 mM beta-mercaptoethanol at 37 degrees C. Apolipoprotein A-I did not activate the enzyme and bovine serum albumin bound monomeric substrate and interfered with the fluorescence assay. Under similar reaction conditions, bee venom phospholipase A2 was almost 100-fold more reactive than LCAT.

Humans↗
PubMed1983

Characterization of lecithin:cholesterol acyltransferase from human plasma: II. Physical properties of the enzyme.

The physical properties of purified human plasma lecithin:cholesterol acyltransferase (LCAT) were investigated by techniques including analytical ultracentrifugation, ultraviolet spectroscopy, electrofocusing, and circular dichroism. The partial specific volume of LCAT was determined by sedimentation equilibrium ultracentrifugation experiments in H2O and D2O solutions (0.702 ml/g). The Mr was 67,000 by sodium dodecyl sulfate (SDS)-gel electrophoresis and 60,000 by sedimentation equilibrium ultracentrifugation. The discrepancy between the two sets of data presumably arose from the glycoprotein nature of the enzyme. Studies of the ultraviolet spectrum indicated that LCAT contained 6.5% (w/w) tyrosine which corresponds to approximately 18 tyrosine residues/mol of LCAT (polypeptide Mr 45,000). Spectrophotometric titration of the ionizable phenolic side chains indicated that nearly all the tyrosine residues were buried at neutral pH while they became gradually exposed at higher pH. The apparent pK of this transition was about 12.0 contrasted with 9.8, the apparent pK of ionization of the free tyrosyl groups.

Centrifugation, Density Gradient↗
PubMed1984

Effects of detergents on the lecithin:cholesterol acyltransferase reaction.

This paper describes the effect of an ionic (sodium dodecyl sulfate; SDS) and a nonionic detergent (Triton X-100) on the substrate and enzyme components of the lecithin: cholesterol acyltransferase (LCAT) reaction. When the enzyme sources (purified or partially purified) or the respective substrates [high-density lipoproteins (HDL) or proteoliposomes] were preincubated with detergents, a consistent trend in LCAT activity was only seen when partially purified LCAT was used as the enzyme source. This trend indicated an approximately 25% increase in enzyme activity over the control when 10(-4) M SDS and 2 X 10(-3)% Triton X-100 were present in the preincubation mixtures, respectively. Those observations suggested that, during the preincubations and subsequent assays, the enzyme (in the presence of detergents) was allowed to dissociate from the endogenous substrate and subsequently interact with the exogenous substrate molecules. Additional experiments utilizing molecular-sieve chromatography with whole plasma and partially purified enzyme also showed that dissociation of LCAT/lipoprotein complexes occurred in the presence of detergent. SDS was also shown to enhance the reaction of LCAT in whole plasma with anti-LCAT antibody in an enzyme-linked immunoassay system, indicating that the detergent treatment facilitated the exposure of additional antigenic sites, perhaps via dissociation of the enzyme from plasma lipoproteins.

Animals↗
PubMed1988

Identification of the active-site serine in human lecithin: cholesterol acyltransferase.

Purified human lecithin:cholesterol acyltransferase (LCAT) was covalently labeled by [3H]diisopropylflourophosphate with concomitant loss of enzymatic activity (M. Jauhiainen and P.J. Dolphin (1986) J. Biol. Chem. 261, 7023-7043). Some 60% of the enzyme was labeled in 1 h. Cyanogen bromide (CNBr) cleavage of the labeled, reduced, and carboxymethylated protein, followed by gel permeation chromatography yielded a 5- to 6-kDa peptide (LCAT CNBr-III) containing at least 60-70% of the incorporated label. Comparison of the amino acid composition of LCAT CNBr-III with that of the CNBr peptides predicted from the LCAT sequence (J. McLean et al. (1986) Proc. Natl. Acad. Sci. USA 83, 2335-2339) indicates that LCAT CNBr-III is peptide 168-220. In 22 cycles of automated Edman degradation of CNBr-III a radioactive derivative was only observed at cycle 14, and of the predicted CNBr fragments only peptide 168-220 contains a serine at position 14 from the amino terminus. Tryptic peptides predicted from the sequence should contain Ser181 at positions 22 and 23 from the N-terminus of fragments 160-199 and 159-199, respectively. On the other hand, Ser216 should be in position 15 from the N-terminus in fragment 202-238. Radiolabel sequencing of the tryptic digest of [3H]diisopropylphosphate-LCAT resulted in recovery of radioactivity in cycles 22 and 23, whereas cycle 15 yielded negligible radioactivity. These results establish that Ser181 is the major active site serine in human LCAT.

Amino Acid Sequence↗
PubMed1976

Alternating current studies of charge carrier transport in lipid bilayers. Pentachlorophenol in lecithin-cholesterol membranes.

Surface and interior electrical properties of lecithin-cholesterol bilayer membranes treated with the uncoupler pentachlorophenol have been determined on the basis of a.c. measurements over a wide range of frequencies (0.02 to 1000 kHZ). The method used depends on accurately determining the resistance of the aqueous solution in series with each individual membrane by extrapolating admittance data into infinite frequency. Loss tangent vs. frequency curves are corrected by subtracting out a loss contribution which is present in untreated membranes and is due, presumably, to dielectric relaxation. The results, which are useful below 100 kHZ, can be fitted to loss tangent curves computed for a three-element equivalent circuit consisting of frequency independent conductance-capacitance pairs, arranged in series to represent surface and interior properties of membranes. Interior conductances agree with net conductances obtained from d.c. measurements. The pH and concentration dependence of surface conductance is consistent with a scheme of transport in which a fixed number of surface binding sites are filled preferentially with neutral pentachlorophenol molecules, which in turn dissociate to supply protons to the aqueous phase. Surface capacitances range from 15 to 90 times that of interior capacitance and show a systematic increase with pentachlorophenol concentration at high pH, and a decrease with concentration at low pH.

Biological Transport, Active↗
PubMed1976

Interactions of the cholesterol side-chain with egg lecithin. A spin label study.

The effect in egg lecithin liposomes of cholesterol and cholesterol analogues with side-chains of reduced length on the order parameters of two steroid spin labels has been studied. Analogues with side-chains shorter than cholesterol by more than three carbon cause significantly less ordering than cholesterol. Liposomes containing a cholesterol analogue in which the side-chain is absent cause very little increase in the ordering of a new sterol spin label in which the nitroxide is incorporated into the side-chain. The results suggest that the sterol side-chain exerts a great influence on membrane rigidity within its immediate environment.

Binding Sites↗