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At least 595 records · Page 33Linked to original sources

PubMed1990

Oxidized LDL increase free cholesterol and fail to stimulate cholesterol esterification in murine macrophages.

Oxidatively modified low density lipoproteins (Ox-LDL) may be involved in determining the formation of foam cells by inducing cellular cholesteryl ester accumulation. We studied the effect of copper oxidized LDL (Ox-LDL) on cholesterol accumulation and esterification in murine macrophages. Ox-LDL (44 micrograms/ml of lipoprotein cholesterol) increased the total cholesterol content of the cells from 29 to 69 micrograms/mg cell protein. Free cholesterol accounted for 85% of this increase. Acetyl LDL (Ac-LDL) (38 micrograms/ml of lipoprotein cholesterol), raised total cellular cholesterol content to a similar extent (76 micrograms/mg cell protein), however only 25% of the accumulated cholesterol was unesterified. When ACAT activity was determined after incubation of J774 cell with Ox- or Ac-LDL, Ox-LDL were 12 times less effective than Ac-LDL in stimulating cholesteryl ester formation. This was not due to an inhibition of ACAT by Ox-LDL since these lipoproteins failed to inhibit pre activated enzyme in cholesteryl ester-loaded macrophages. The uptake of 125I-Ox-LDL: was 175% that of 125I-Ac-LDL, while degradation was only 20%. All together these data suggest an altered intracellular processing of Ox-LDL, which may be responsible for free cholesterol accumulation.

Acetylation↗

PubMed1993

Determination of the pattern of methyl esterification in pectin. Distribution of contiguous nonesterified residues.

A method is described for determining the distribution of contiguous nonesterified galacturonic acid residues within pectins. First, the esterified galacturonic acids are converted to galactose by reduction with sodium borohydride, then the glycosidic linkages of the resulting galactose residues are cleaved selectively by liquid HF solvolysis. Separation and quantitation of the resulting galacturonic acid containing oligomers reveals the proportion of each stretch of contiguous nonesterified galacturonic acid residues in the original pectin. The distribution of nonesterified GalA in a pectin fraction obtained from cotton suspension culture cell walls with approximately 50% esterification appears to be far from random.

Borohydrides↗

PubMed1985

Influence of platelet activation factor and prostaglandins on cholesterol esterification in human plasma.

Prostaglandin E1 (PGE1) and platelet activation factor (PAF) were found respectively to activate or to inhibit cholesterol esterification in whole plasma but not in lipoprotein-deficient plasma. It is suggested that these effects are mediated by the interaction of PGE1 and PAF with high-density lipoproteins [(1984) FEBS Lett. 173, 291-294]. Possible physiological implications of these findings are discussed.

Alprostadil↗

PubMed1990

Kinetic study of esterification by immobilized lipase in n-hexane.

The kinetic of the esterification of oleic acid by ethanol catalyzed by immobilized lipase of Mucor miehei in n-hexane as a solvent has been completely studied. The kinetics of the reaction are suggested to agree with a Ping-Pong Bi Bi mechanism in which only inhibition by excess of ethanol has been identified. Values of all apparent kinetic parameters were computed. No evidence of any significant external diffusional limitation which could account for these values has been detected. Optimization of water content through distribution ratio of water between solvent and support was examined.

Enzymes, Immobilized↗

PubMed1982

Rate of LCAT-mediated cholesterol esterification and serum lipids during etiroxate therapy in hyperlipoproteinemia.

Changes in the rate of the plasma cholesterol ester production mediated by lecithin: cholesterol acyltransferase (LCAT, E.C. 2.3.1.43) were examined in 15 patients suffering from types II and IV HLP who had been treated for 14 weeks with etiroxate. Whereas the plasma cholesterol concentration decreased significantly only in the initial phase of the therapy, the rate of cholesterol esterification increased gradually and attained at the end of the study a value exceeding by 50% the initial level. The final fractional turnover rate nearly equalled that characteristic for the control group of healthy subjects, in spite of the fact that the concentration of plasma cholesterol in the diseased subjects was higher by 50-100%. Triglyceride concentration decreased only transitorily in the course of the therapy with etiroxate. It is concluded that etiroxate is likely to normalize the rate of cholesterol turnover in the endogenous pool.

Body Weight↗

PubMed1990

Investigation of lipid transfer in human serum leading to the development of an isotopic method for the determination of endogenous cholesterol esterification and transfer.

The rate at which radioactivity appeared in cholesteryl esters (CE) in whole serum and in very low density lipoproteins (VLDL) and low density lipoproteins (LDL) when radioactively labelled free cholesterol (FC) was incubated with serum was investigated. At 4 degrees C equilibration of radioactive FC with native FC occurred, but there was no conversion to CE. At 37 degrees C CE mass increased in parallel with radioactivity in CE both in whole serum and VLDL/LDL. Incubation at 37 degrees C with an inhibitor of lecithin cholesterol acyl transferase (LCAT) abolished the increase in the total CE radioactivity and mass in serum. Transfer of CE from high density lipoprotein (HDL) to VLDL/LDL, however, continued to occur. An assay for LCAT and for cholesteryl ester transfer protein (CETP) was developed, which employed the increases in radioactive CE in whole serum and VLDL/LDL during a single incubation as indices of LCAT and CETP activity, respectively. Determination of the initial serum FC concentration allowed the expression of these activities in nmol/ml per h. References ranges were established in 62 fasting normolipidaemic men and women and increases in both LCAT and CETP were found following a fatty meal. The experiments thus provided further information about the carrier-mediated transfer of CE from its site of esterification on HDL to VLDL/LDL and formed the basis of a relatively simple assay, which has advantages over previously published methods and which may be used in clinical and epidemiological studies to elucidate the role of CETP and LCAT in atherosclerosis.

Apolipoproteins↗

PubMed1982

Influence of progesterone on the initial rate of cholesterol esterification in rat plasma.

The effect of progesterone on the initial rate of cholesterol esterification in rat plasma was measured after daily injections of the hormone or following addition of progesterone in vitro. The administration of progesterone did not modify the lecithin: cholesterol acyltransferase (LCAT) activity nor the progress of the enzyme reaction with time. When increasing concentrations of progesterone were added to the medium the percentage of cholesterol esterified per minute decreased progressively. The addition of progesterone also decreased the slope of the time-course reaction. It is suggested that the inhibition of the LCAT activity due to the presence of the hormone would be masked by an increased hepatic production of the enzyme and/or by the alterations that the hormonal treatments produced in the plasma lipid levels.

Animals↗

PubMed1983

Esterification of monohydroxyfatty acids into the lipids of a macrophage cell line.

Cells of a mouse macrophage-like tumor cell line, J774.2, were incubated with 0.6 microM radiolabeled mono- and di-hydroxyfatty acids. Monohydroxyfatty acid products of the neutrophil and platelet lipoxygenase pathways (5-HETE, 15-HETE, and 12-HETE) were rapidly taken up (42-64% of the counts cell associated at 1 min) and esterified into triglycerides and phospholipids. 5-HETE and 12-HETE were found in triglycerides and distributed among phospholipid classes while 50% of added 15-HETE was esterified into phosphatidyl inositol. Treatment of phospholipids from cells incubated with 5-HETE, 12-HETE, and 15-HETE with phospholipase A2 resulted in release of the respective monohydroxyfatty acid. HHT, a monohydroxyfatty acid product of the cyclooxygenase pathway, was taken up and esterified more slowly than the lipoxygenase products. In addition, HHT was not released when the phospholipids from cells incubated with HHT were treated with phospholipase A2. LTB4, a dihydroxyfatty acid product of neutrophil lipoxygenase, was not taken up by J774.2 cells. The unique patterns of uptake and intracellular distribution of the different monohydroxyfatty acids suggests that the enzymes involved in the esterification of these compounds have substrate specificity and may also relate to the specific biologic effects of these compounds.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗

PubMed1985

Incorporation of 5,8,11,14-eicosatetraynoic acid (ETYA) into cell lipids: competition with arachidonic acid for esterification.

5,8,11,14-eicosatetraynoic acid (ETYA), a widely used inhibitor of cyclooxygenase and lipoxygenase, inhibited the incorporation of 14C-arachidonic acid into cell lipids of the murine thymoma EL4 whereas oleic acid had no effect. Inhibition appeared to result from the ability of ETYA to compete with arachidonic acid for esterification enzymes and to be itself incorporated into cell lipids. The positional specificity for ETYA incorporation was similar to that of arachidonic acid. ETYA, but not oleic acid competed with arachidonate for activation by a selective arachidonoyl CoA synthetase in lymphocytes. This may explain in part the apparent specificity of effects seen on incorporation into whole cells. In addition ETYA, unlike other arachidonate analogs tested previously, caused significant inhibition of the nonselective acyl CoA synthetase in lymphocytes. These results are discussed with respect to the use of ETYA to examine the role of intrinsic arachidonic acid metabolism in cellular processes.

5,8,11,14-Eicosatetraynoic Acid↗

PubMed1981

Solution characterization of starch nicotinates with different degrees of esterification.

A series of starch-nicotinic acid copolymers with a degree of esterification ranging from about 15% to about 90% was prepared, and the stability in solution of two representative samples of the series was tested. The variation of some physico-chemical characteristics in the series was examined by solubility tests, viscometry and refractometry, and found to be not simply correlatable to the nicotinylation degree.

Esters↗

PubMed1991

Substrate specificity of alpha-chymotrypsin-catalyzed esterification in organic media.

11 amino acid derivatives were tested as alpha-chymotrypsin substrates in the esterification reaction with methanol in organic media. The reactions were carried out in water-saturated ethyl acetate and in acetonitrile containing 4% water. alpha-Chymotrypsin adsorbed on Celite was used as a catalyst. From initial reaction rate measurements, the Michaelis-Menten parameters Vmax and KM were determined. All the amino acid derivatives tested were esterified, and the highest values of kcat/KM were obtained with the N-acylated aromatic amino acids. Correlations between Michaelis-Menten parameters and physical properties of the substrates such as molar refractivity (MR) and log P were deduced. The results show that the specificity of the alpha-chymotrypsin towards the side chain of the amino acids in organic media is the same as that in aqueous media. However, the specificity towards the N-protecting group is opposite to that in water, so the reaction medium affects the interaction of this part of the molecule with the enzyme to a large extent.

Acetates↗

PubMed1986

Effect of monensin and nocodazole on the intestinal lipid esterification in mouse jejunal organ culture.

The ability of mouse jejunal explants to esterify a lipid emulsion containing oleic acid, palmitic acid and monopalmitin has been studied in different in vitro experimental conditions. The incubating lipid solution must have a minimum volume for obtaining optimal triglyceride esterification by the cultured intestinal mucosa. In our incubating conditions the exchange of oleic for palmitic acid does not significantly modify the amount of lipids esterified by the explants in 15 min. Monensin or nocodazole, added to the culture medium of intestinal explants for 3 hr, significantly change the amount of lipids esterified and secreted. The inhibition observed after nocodazole treatment disappears, however, when the explants are rinsed and the culture is allowed to continue for an additional 3 hr in a drug-free medium. These results suggest that the regulation of lipid metabolism can be studied in organ culture.

Animals↗

PubMed1986

Lipid esterification and secretion by the mouse intestine in organ culture.

Explants of adult mouse jejunum were cultured for different time periods and incubated in presence of a lipid diet emulsified by sodium taurocholate or complexed with albumin. The esterification of fatty acids and the secretion of triglycerides and phospholipids were measured and compared to the lipid absorption observed in vivo after the perfusion of the same diet. The results show that, in vitro, the enterocytes esterify the fatty acids present in the medium and secrete them with a yield improving during the culture and even better than the absorption observed in the in vivo experiments.

Alkaline Phosphatase↗

PubMed1981

The equilibrium constants and enthalpy changes for the esterification of glycine by ethanol in water and ethanol- water mixtures.

Equilibrium constants, defined on the basis of the moles of all reactants and products including water, were found to be 4.6, 1.0 and 0.8 for the esterification of the glycinc cation at 20 degrees in a dilute aqueous sytem, and systems having 0.5 : 1 and 1 : 1 molar ratios of ethanol to water, respectively. When corrections were made for deviations from ideality a value of 5 +/- 1 was obtained for all three systems. Enthalpy changes were determined calorimetrically for the dilute aqueous and equimolar ethanol-water systems, and in each case was close to 1 kcal mole(-). The entropy change was calculated as 6 cal mole(-1) deg(-1).DeltaG(0') for the hydrolysis of the glycine ethyl ester cation at 20 degrees and pH 7 was calculated as -7.5 kcal mole(-1).

Journal Article↗

PubMed1987

A comparative study of the rate-limiting enzymes of cholesterol synthesis, esterification and catabolism in the rat and rabbit.

1. The rat and rabbit are amongst the animal models most widely used in the study of human atherosclerosis, a disease state correlating with disturbances in cholesterol metabolism. 2. In order to relate the key regulatory enzymes of cholesterol synthesis, esterification and catabolism in the rat and rabbit to their differing degree of susceptibility to atherosclerosis, enzyme levels and their properties were determined in liver and intestine of both species. 3. Hepatic HMG CoA reductase and cholesterol 7 alpha-hydroxylase levels were significantly higher in the rat than in the rabbit, while intestinal HMG CoA reductase activity in the two species was comparable. Conversely, the capacity to esterify cholesterol as measured by ACAT activities was considerably greater in both sites in the rabbit compared to the rat. 4. The data suggest that differences in the key regulatory enzymes of cholesterol metabolism in both liver and intestine may reflect different methods of cholesterol utilization in the two species.

Animals↗

PubMed2005

Action pattern of Valencia orange PME de-esterification of high methoxyl pectin and characterization of modified pectins.

Valencia pectinmethylesterase (PME) fractions, B-PME, containing 36 and 13 kDa protein bands and U-PME, containing a 36 and 27 kDa protein bands, were used to de-esterify original pectin (O-Pec) from 73% degree of esterification (%DE) to 63% (B-Pec) and 61% DE (U-Pec), respectively. Most O-Pec eluted from ion exchange chromatography at low salt concentration and a smaller component eluted at higher ionic strength. B-Pec and U-Pec eluted as one broad peak at higher ionic strength. PME modification did not change molecular weight: O-pectin (134,000 g/mol), U-Pec (133,850 g/mol), and B-Pec (132,250 g/mol). The NMR signal of GG and GGG increased after modification, whereas the signal of EE and EEE decreased. The negative zeta-potential increased with pH for all pectins. U-PME and B-PME created differently modified pectins that vary in degree and length of multiple attacks and fraction of the pectin population that was modified.

Carboxylic Ester Hydrolases↗

PubMed2005

How does the N-acylation and esterification of amphotericin B molecule affect its interactions with cellular membrane components-the Langmuir monolayer study.

This work presents the results of Langmuir monolayers study of two amphotericin B derivatives obtained by N-acylation (N-acetylamphotericin B, Ac-AmB) and esterification (amphotericin B methyl ester, AME) of the parent AmB molecule. The main objective of present investigations was to examine the strength and nature of interactions of Ac-AmB and AME with natural membrane components as compared to AmB, and verify the monolayer results with biological studies in vitro. Our experiments were based on surface pressure-area measurements of mixed monolayers formed by the investigated antibiotics and sterols/DPPC. The interactions were analyzed with the following dependencies: compression modulus-surface pressure, mean molecular area-composition, excess molecular area-composition and excess free energy-composition plots. It has been found that both Ac-AmB and AME form monolayers of a liquid expanded state and their stability is highest as compared to AmB films. The investigated compounds mix in monolayers with natural membrane components within the whole range of the antibiotic mole fraction. The quantitative analysis of the interactions of the investigated antibiotics with sterols and DPPC as well as sterols/DPPC interactions allow us to verify the monolayer results with biological results. A good correlation between both kinds of studies has been found.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed2004

Exobasidium vexans infection of Camellia sinensis increased 2,3-cis isomerisation and gallate esterification of proanthocyanidins.

Infection of leaves of tea (Camellia sinensis (Kuntze) L, cv TRI 2025) which was susceptible to blister blight (Exobasidium vexans Massee), resulted in a shift of the proanthocyanidin stereochemistry away from 2,3-trans (e.g. catechin and gallocatechin) and towards 2,3-cis (e.g. epicatechin and epigallocatechin). Infection also resulted in increased gallic acid esterification of the initiating subunits of proanthocyanidins. This was shown by both mass spectroscopy and phloroglucinolysis. Proanthocyanidins isolated from healthy tissue had a predominantly 2,3-trans stereochemistry which accounted for 53% and 61% of the total initiating and extension units of proanthocyanidin, respectively. Conversely in infected tissue, proanthocyanidin subunits with a 2,3-trans stereochemistry accounted for 26% and 40% of the total initiating and extension units, respectively. Infection had little impact on the hydroxylation state of the B-rings of proanthocyanidins. The products of acid hydrolysis under oxidative conditions had a slight excess of di-hydroxylated B-rings with cyanidin accounting for 58.3+/-0.05% and 60.4+/-0.2% of the total anthocyanidin recovered following hydrolysis of proanthocyanidin isolated from infected and healthy leaves, respectively. Similar results were obtained by phloroglucinolysis.

Basidiomycota↗