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PubMed1990

Rapid labeling of lipoproteins in plasma with radioactive cholesterol. Application for measurement of plasma cholesterol esterification.

In order to efficiently and rapidly label lipoproteins in plasma with [3H]cholesterol, micelles consisting of lysophosphatidylcholine (lysoPC) and [3H]cholesterol (molar ratio, 50:1) were prepared. When trace amounts of these micelles were injected into plasma, [3H]cholesterol rapidly equilibrated among the plasma lipoproteins, as compared to [3H]cholesterol from an albumin-stabilized emulsion. The distributions of both [3H]cholesterol and unlabeled free cholesterol in plasma lipoproteins were similar in labeled plasma samples. This method of labeling can be used for the measurement of cholesterol esterification, or lecithin:cholesterol acyltransferase activity, in small amounts (20-40 microliters) of plasma samples.

Cholesterol↗

PubMed1988

UV irradiation and topical vitamin A modulate retinol esterification in hairless mouse epidermis.

The formation of fatty acyl esters of retinol, the major form of vitamin A in epidermis, is catalysed by microsomal enzymes. To study the regulation of retinol esterification, we exposed hairless mice to ultraviolet (UV) irradiation which destroys vitamin A and to topical retinol treatment. Vitamin A (retinol and retinyl esters) in serum and epidermis was analysed by high-performance liquid chromatography at 0-12 days after a single irradiation with UVB (280-320 nm; 0.34 J/cm2) or UVA (320-400 nm; 1.0 J/cm2). The immediate vitamin A reducing effects of UVB and UVA were similar, but UVB elicited a more rapid replenishment of epidermal vitamin A with a corresponding transient depletion of serum retinol after 2-3 days. The activity of retinyl ester synthetase, measured by an in vitro radiochemical assay, was unaffected by the irradiations. By contrast, the acyl-CoA:retinol acyltransferase (ARAT; EC 2.3.1.76) activity increased to 167% on the 2nd day after UVB-irradiation and to 124% after topical retinol, but was otherwise quite constant. The UVB- and retinol-induced ARAT activity was less dependent on exogenous palmitoyl-CoA than that of control microsomes and experiments indicated that this might be due to an increased endogenous concentration of long-chain acyl-CoA in the microsomes. We conclude that extreme variations in the vitamin A supply to epidermis, such as a rapid influx of unesterified retinol, may modulate the epidermal ARAT activity.

Acyltransferases↗

PubMed1988

Effects of somatostatin on the insulin- and gastric inhibitory polypeptide-stimulated fatty acid esterification in rat adipose tissue.

Relations exist between insulin, somatostatin (S) and gastric inhibitory polypeptide (GIP) for the reciprocal control of their secretion but also for their role in lipid metabolism. In the present experiment, we studied the effects of somatostatin on fatty acid incorporation into epididymal adipose tissue (FIAT) of Wistar rats when it was stimulated by insulin and GIP. Cyclic somatostatin-14 was used at physiological (S1 : 50 pg/ml, S2 : 200 pg/ml) and supraphysiological (S3 : 666 pg/ml) concentrations whereas insulin and GIP were used at postprandial levels (100 microU/ml and 2 ng/ml respectively). Results were expressed as percent of basal incorporation (without any hormones). Somatostatin inhibited basal FIAT at all concentrations and totally abolished the insulin-stimulated FIAT (from 106.4 +/- 2.3 per cent with insulin alone to 92.6 +/- 2.5 per cent with S3, P less than 0.001). GIP enhanced the insulin-stimulated FIAT from 106.4 +/- 2.3 per cent to 113 +/- 3.0 per cent (P less than 0.01). On the contrary, when somatostatin was added with GIP and insulin, FIAT decreased to 102.3 +/- 2.5 per cent for S1 (P less than 0.01) and to 98.2 +/- 2.6 per cent for S3 (P less than 0.001). These results indicate that somatostatin totally inhibits the fatty acid esterification induced by insulin and in the same proportions that induced by insulin associated with GIP. Somatostatin is not only an inhibitor of the secretion of these hormones but also a regulator of their biological action in adipose tissue.

Adipose Tissue↗

PubMed1986

p-Hydroxymercuribenzoic acid inhibits arachidonic acid esterification into two distinct pools and stimulates insulin release in intact rat islets.

Activation of an islet phospholipase A2 may contribute to glucose-induced insulin release. In order to simulate the accumulation of the resultant hydrolytic products (arachidonic acid, AA; its lipoxygenase-derived oxygenation product 12-hydroxyeicosatetraenoic acid; and lysophospholipids) without many of the other concomitants of beta cell activation, we studied the effects on intact rat islets of p-hydroxymercuribenzoic acid (PHMB), which inhibits the reacylation of lysophospholipids with AA in other cell types. PHMB inhibited in a dose-responsive fashion (-90% at 500 microM) the incorporation of [3H]AA into a "basal" pool or pools whose release and reuptake mechanisms appeared to be largely energy- and Ca++-independent (resistant to inhibition by mannoheptulose, antimycin A or CoCl2); reciprocally, islets prelabeled with [3H]AA accumulated an increased amount of [3H]-12-hydroxyeicosatetraenoic acid (twice basal at 200 microM PHMB and three times basal at 500 microM) when reacylation of any [3H]AA released basally at 1.7 mM glucose was inhibited. PHMB also blocked (by up to 99% at 500 microM) the incorporation of [3H]AA into a functionally defined, glucose-stimulated compartment of fatty acid (tightly coupled to the islet 12-lipoxygenase) whose release and reuptake required metabolic energy and Ca++. It was also demonstrated that PHMB inhibited the esterification of [3H]AA (at low or high glucose concentrations) into specific phospholipids in islet membranes. In parallel with these alterations in lipid metabolism, PHMB caused rapid, potent and reversible increments in insulin release with a threshold concentration (about 25 microM) identical to that inhibiting AA fluxes. PHMB both initiated release (at 1.7 mM glucose) and potentiated the effects of islet fuels (16.7 mM glucose or 15 mM alpha-ketoisocaproic acid). Thus, pharmacologic manipulation of the AA reuptake mechanism is a new approach to unmask potential roles in insulin release of phospholipid hydrolysis products from different lipid pools and in the absence or presence of phospholipase A2 activation.

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

PubMed1987

Effect of lipid-free milk on prostaglandin synthesis and lipid esterification in the young rabbit aorta.

The effect of lipid-free human milk on prostaglandin synthesis and lipid esterification by [14C]-arachidonic acid was examined in one week-old rabbit aortas, in vitro. In the presence of albumin, lipid-free milk increased arachidonic acid incorporation into aortic phospholipids, cholesterol esters and triglycerides but not into mono- and diglycerides. Lipid-free milk also increased the conversion of arachidonic acid into aortic 6-keto-PGF1 alpha, but not into PGF2 alpha or PGE2.

Animals↗

PubMed1987

Cell cycle-dependent methyl esterification of lamin B.

Previous work from this laboratory has shown that approximately 24 proteins are reversibly modified by methyl esterification in a mouse lymphoma cell line. Here, we analyze several mouse tissues as well as other mouse, hamster, and human cell lines and find that many protein-methyl esters are ubiquitous while others show apparent tissue specificity. One of the modified proteins is identified by cellular localization and immunological detection as lamin B, a nuclear envelope structural protein which undergoes depolymerization during mitosis. The average stoichiometry of methylation is at least 0.5 methyl groups per lamin B molecule as determined by radioactive incorporation. By immunoblotting, however, demethylation appears to result in a gain of two negative charges suggesting the loss of two neutral methyl esters producing two carboxylic acid groups per molecule. By comparing mitotic and interphase cells, lamin B is found to be demethylated in mitosis while most other methyl esterified proteins show no appreciable cell cycle dependence. In addition to the correlation with cell cycle, it is shown that lamin B does not incorporate radioactive methyl esters in intact mouse brain tissue yet can do so if the cells are lysed. Analysis of lamin B charge by immunoblotting after isoelectric focusing indicates that this protein is fully methylated in brain suggesting that turnover of methyl groups in intact brain tissue is inhibited. We propose that methylation of lamin B may be involved in the control of disassembly and reassembly of the nuclear envelope during mitosis. If this were the case, the apparent lack of methyl group turnover in brain would be consistent with the inability of those cells to divide.

Animals↗

PubMed1987

[Action of cytoplasmic factors from the regenerating liver on cholesterol esterification in the blood serum of rats with tetrachloromethane liver damage].

The effect of proliferation stimulating factors (PSF) obtained from regenerating liver on the cholesterol esterification in blood serum under deep tetrachloromethane intoxication has been studied in experiments with white rats. Three phases in dynamics of cholesterol content in blood serum have been picked out after a single tetrachloromethane injection. The content of total cholesterol and cholesterol esters reduces during the first phase (24 h), during the second phase (3-7th day) it increases and during the third phase (15th day) these values become normal. PSF injection does not produce any influence on the nature of blood cholesterol under deep tetrachloromethane intoxication, but stimulates the processes of cholesterol ester formation in blood serum.

Animals↗

PubMedDate not supplied

[Evaluation of a pectin with a low degree of esterification as a prophylactic agent in lead poisoning].

In experiments with rats, which were undergoing priming by mouth with an acetic lead solution at the rate of 6 mg/day for 1 1/2 month, the prophylactic effect of apple pectin esterified to the degree of 26 per cent (doses 36 and 72 mg) and of 32 per cent (doses of 216 and 432 mg) was evaluated. The best prophylactic effect was found to produce pectin with a 32 per cent esterification degree, but in some of rats dysfunction of the gastro-intestinal tract was noted.

Animals↗

PubMed1980

[Esterification of cholesterol in patients with renal transplants. Determination of lecithin:cholesterol-acyl-transferase (LCAT) activity].

In man, cholesterol esterification is controlled by lecithin:cholesterol-acyl-transferase (LCAT), which is a key-role enzyme of lipid metabolism. Though LCAT is synthesized by the hepatocytes, its activity seems to be linked to the kidney: in fact, LCAT activity is lowered in uremic and anephric subjects, and probably also in long-term haemodialysis patients. On the contrary, in successfull renal allografts we found fully restored LCAT activity. But physiopathological mechanisms underlying relationships between LCAT and kidney are still unclarified.

Cholesterol↗

PubMed1993

Methyl esterification of C-terminal leucine residues in cytosolic 36-kDa polypeptides of bovine brain. A novel eucaryotic protein carboxyl methylation reaction.

Incubation of cytosolic extracts of bovine brain with S-adenosyl[methyl-3H]methionine results in the predominant [3H]methyl esterification of a 36-kDa polypeptide. This reaction appears to be distinct from any of the three known types of protein carboxyl methylation reactions previously established. We show here that the methylated 36-kDa polypeptide is a component of a cytosolic protein with a native molecular mass estimated at 178 kDa by gel filtration chromatography. The methyl group is not stable on the protein and is lost as [3H]methanol with a half-life of about 180 min at pH 7.0, 37 degrees C. The methyltransferase responsible for this reaction is a cytosolic protein with a native molecular mass of about 40 kDa that is readily separated from the well described protein-L-isoaspartate (D-aspartate) O-methyltransferase (EC 2.1.1.77). The methyl ester linkage is cleaved by carboxypeptidase Y, suggesting that the 36-kDa polypeptide is methylated on its C-terminal carboxyl group. Extensive digestion of gel-purified 3H-methylated 36-kDa polypeptide with trypsin and leucine aminopeptidase results in a radioactive product that co-chromatographs with authentic L-leucine methyl ester in reverse phase high performance liquid chromatography (HPLC), thin layer chromatography, thin layer electrophoresis, and high resolution-sulfonated polystyrene cation-exchange chromatography. Additionally, the o-phthalaldehyde/beta-mercaptoethanol-derived isoindole derivative of the 3H digestion product co-migrates on HPLC with the corresponding isoindole for L-leucine methyl ester. We demonstrate that a similar methylation system is present in yeast Saccharomyces cerevisiae but not in the bacterium Escherichia coli. These results provide evidence for a new type of reversible posttranslational modification reaction that may function to modulate the activities of its methyl-accepting substrates.

Amino Acid Sequence↗

PubMed1995

Correlation of teichoic acid D-alanyl esterification with the expression of methicillin resistance in Staphylococcus aureus.

Methicillin-susceptible and -resistant isolates of Staphylococcus aureus, including a teichoic acid-deficient mutant, were examined under varying physiological conditions for their degree of teichoic acid and lipoteichoic acid D-alanyl esterification. Methicillin-resistant strains grown in the presence of methicillin and NaCl possessed significantly decreased amounts of D-alanyl ester when compared with methicillin-susceptible isolates. These strains also exhibited reduced autolysis. An autoradiographic procedure was used to detect mutants, isolated by Tn917 and nitrosoguanidine mutagenesis of methicillin-susceptible strains, which were defective in D-alanyl ester formation. The quantitative uptake of D-[14C]alanine in these mutants was determined and the effect of methicillin on the growth and viability of each mutant was compared with the wild-type strain. S. aureus mutant strains, defective in the uptake and incorporation of D-alanine, were shown to exhibit slightly reduced autolysis and an enhanced expression of methicillin resistance.

Alanine↗

PubMed1997

Fractional esterification rate of cholesterol in high density lipoprotein is correlated with low density lipoprotein particle size in children.

Small low density lipoprotein (LDL) particles are thought to be more atherogenic than larger LDL particles, although this association may depend on plasma triglyceride (TG) and high density lipoprotein (HDL) levels. To help prevent coronary artery disease (CAD), it may be useful to understand risk factors during childhood and adolescence. In the present study, we evaluated low density lipoprotein particle size (LDL-size) by 2-16% gradient gel electrophoresis in 70 healthy children (30 boys and 40 girls) along with conventional lipid and lipoprotein parameters which are thought to affect LDL-size. The fractional and molar esterification rates (FER and MER) of cholesterol in plasma and HDL were also determined. As expected, plasma levels of TG, HDL-cholesterol (HDL-C) and apoA-I were closely associated with LDL-sizes in both sexes (boys: r = -0.694, 0.708 and 0.701, girls: r = -0.579, 0.551 and 0.539, P < 0.001). However, a closer association was found between FER in HDL (FER(HDL)) and LDL-size (boys: r= -0.874, girls: r= -0.642, P < 0.001). In a stepwise multiple regression analysis, FER(HDL) alone accounted for 76% and 41% of the variability in LDL-size in boys and girls, respectively. MER in HDL accounted for additional 4% and 19% in boys and girls, respectively. Other parameters, including plasma TG, HDL-C and apoA-I had no significant additional effects. Thus, the determination of FER(HDL) is useful to predict the particle size of LDL in children.

Adolescent↗

PubMed1997

Expression of human lecithin:cholesterol acyltransferase in transgenic mice: effects on cholesterol efflux, esterification, and transport.

Human lecithin:cholesterol acyltransferase (LCAT) is a key enzyme in the plasma metabolism of cholesterol and is postulated to participate in a physiologic process called reverse cholesterol transport. We have used transgenic mice expressing the human LCAT transgene to study the effect of increased plasma levels of LCAT in each of the proposed steps involved in the reverse cholesterol transport pathway. High density lipoprotein (HDL) from LCAT transgenic mice was 44% more efficient than control mouse HDL in the efflux of cholesterol from human skin fibroblasts. Esterification of cell-derived cholesterol was also markedly increased in mice expressing the human LCAT transgene. The rate of plasma clearance of HDL cholesteryl ester was virtually the same in both types of animals whereas the HDL cholesteryl ester transport rate was significantly increased in mice expressing the human LCAT transgene (152.3 +/- 16.9 micrograms/h vs. 203.1 +/- 30.9 micrograms/h in control and transgenic mice, respectively). Liver cholesteryl ester uptake was significantly increased in mice expressing human LCAT (58.0 +/- 1.4 micrograms/h/g liver vs. 77.9 +/- 1.7 micrograms/h/g liver in control and transgenic mice, respectively). These studies indicate that LCAT modulates the rate by which cholesterol is effluxed from cell membranes onto HDL, esterified, and transported to the liver.

Animals↗

PubMed1976

Increased cholesterol content and esterification in rabbit aortic medial cells cultured in hyperlipidemic serum.

Cells of early atherosclerotic lesions have an increased content of cholesteryl esters and enhanced rate of cholesterol esterification. The present study was carried out to elucidate whether these changes could be reproduced in a purely in vitro system. Cultures of rabbit aortic medial cells were incubated in a medium containing 10% of either normal rabbit serum (control cells) or serum from rabbits with cholesterol-induced hyperlipidemia (hyperlipidemic cells). The incorporation rate of [1-14C]oleate into cellular cholesteryl esters increased two- to threefold after four hours' incubation with hyperlipidemic serum and remained elevated during the rest of the eight days' study. After seven days' incubation the hyperlipidemic cells incorporated significantly more (+13%) oleate into triglycerides and significantly less (-15%) oleate into phospholipids than did the control cells. Cholesteryl ester content of the hyperlipidemic cells rose steeply for about two days, with a slower rise thereafter. In hyperlipidemic cells the esterified cholesterol content was significantly higher (315 ng/mug DNA) than in the control cells (79 ng/mug DNA). Hyperlipidemic cells showed a slow but significant rise of free cholesterol as well (from 1.15 mug/mug DNA in control to 1.50 mug/mug DNA). The results indicate that lipid changes resembling those in early atherosclerotic lesions can be brought about in vitro 0y treatment of aortic cells with hyperlipidemic serum.

Animals↗

PubMed1976

Retinyl palmitate, a major retinyl ester in rat testis seminiferous tubules. II. The Sertoli cell, site of retinol esterification.

The study was designed to 1) isolate and quantitate retinyl esters normally present in the testis seminiferous tubules (ST) and 2) determine whether the Sertoli (SE) cells in the ST have the enzyme system necessary to esterify retinol. In the first study testes from normal adult male rats were removed, the ST were isolated mechanically and retinol was extracted and separated into free and retinyl esters in a prestandardized alumina column. The fraction containing retinyl esters was hydrolyzed, and the fatty acid composition was determined gas chromatographically. The results showed that retinyl palmitate was the major retinyl ester in the testis ST constituting almost 55% of the total esters. In the second study adult male rats were given Busulfan (1,4, dimethylsulfonoxybutane) intraperitoneally twice six weeks apart. At the end of six weeks following injection, the testes from a few animals were examined histologically, and the results showed that Busulfan treatment destroyed the germinal epithelium completely but had no effect on the structural integrity of the SE cells. Labeled retinol (free) mixed in rat albumin solution was injected intratesticularly (in vivo study) or incubated (in vitro study) with ST which had been isolated from the testes of rats treated with Busulfan. The results of the studies indicate that labeled retinol (free) was converted to retinyl esters in the ST. Since the ratio of conversion of free retinol (labeled) to retinyl esters remained constant in the treated ST (which contained only Sertoli cells, the germinal epithelium having been destroyed) and in the control ST (which contained both Sertoli cells and germinal epithelium), we conclude that the Sertoli cells are the site of retinol esterification in the testis ST.

Animals↗

PubMed1976

Coenzyme-A-dependent esterification of cholesterol in rat intestinal mucosa.

Rat intestinal mucosa contains an enzyme which catalyses the esterification of cholesterol. The enzyme is CoA-dependent and probably an acyl-CoA: cholesterol acyltransferase (ACAT) (E.C.2.3.1.26). Maximal activity in vitro is obtained when long chain acylcarnitines, CoA and carnitine palmityltransferase are used as an acyl-CoA generating system. The enzyme is localized in the microsomal fraction, has a pH optimum between 6.4-7.2, and oleate is the preferred acyl group. The activity of the enzyme is highest in the proximal jejunum, and has a capacity that can account for all cholesteryl esters found in intestinal rat lymph.

Acetyl Coenzyme A↗

PubMed1999

Differential absorption and esterification of dietary long-chain fatty acids by larvae of the dragonfly, Aeshna cyanea.

In order to evaluate whether dietary long-chain fatty acids were differentially absorbed, Aeshna cyanea larvae received 5 microliters oral doses containing combinations of two radiolabeled fatty acids at nearly equal radioactive and nmolar concentrations: (1) 3H-oleic and 14C-palmitic acids; (2) 3H-oleic and 14C-stearic acids; and (3) 3H-palmitic and 14C-stearic acids. After 3 h or 1 day, hemolymph samples, midgut tissue, midgut contents and fat body tissue were collected and assayed for labeled fatty acids. The 3H/14C ratios indicated that there was a preference for absorption of the monounsaturated oleic acid over both saturated palmitic and stearic acids and that the shorter palmitic acid was absorbed at a higher rate than the longer stearic acid. There were also differences in the 3H/14C ratios of the various lipid classes of the midgut wall, hemolymph, and fat body that reflected differential esterifications and transport of these fatty acids.

Absorption↗

PubMed2001

Efficient preparation of (R)-alpha-monobenzoyl glycerol by lipase catalyzed asymmetric esterification: optimization and operation in packed bed reactor.

Optically active (R)-alpha-monobenzoyl glycerol (MBG) was synthesized by Candida antarctica lipase B (CHIRAZYME L-2) catalyzed asymmetric esterification of glycerol with benzoic anhydride in organic solvents. Various conditions, such as the type and composition of the organic solvent, water content of the system, reaction temperature, and concentrations of the substrates were systematically examined and optimized in screw-capped test tubes with respect to both the reaction rate and the enzyme selectivity. 1,4-Dioxane was found to be the best solvent and no additional water was needed for the system. The optimum temperature was around 30 degrees C, while the most suitable substrate concentrations were 100 mM each for glycerol and benzoic anhydride, respectively. However, when excessive anhydride (e.g., 200 mM) was used, the produced MBG could be further transformed into 1,3-dibenzoyl glycerol (DBG) by the same enzyme with a priority to (S)-MBG, resulting in a significant improvement of the product optical purity from ca. 50-70% e.e. Under optimal conditions (100 mM glycerol, 100-200 mM benzoic anhydride, dioxane, 25-30 degrees C), the enzymatic synthesis of (R)-MBG was successfully operated in a packed-bed reactor for about 1 week, with an average productivity of 0.79 g MBG/day/g biocatalyst in the case of continuous operation and 0.94 g MBG/day/g biocatalyst in the case of semicontinuous operation. After refinement and preferential crystallization of the crude product, (R)-MBG could be obtained in an almost optically pure form (>98% e.e.).

Benzoates↗