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At least 343 records · Page 19Linked to original sources
PubMed1986

[Changes in the biosynthesis, esterification and efflux of cholesterol in fibroblasts in culture from patients with Niemann-Pick disease type C].

Cholesterol synthesis, esterification and efflux have been comparatively studied in control fibroblasts and in fibroblasts from patients with Niemann-Pick disease type C (NPC). Sterol synthesis was markedly increased in NPC cells as compared to controls, either in whole medium or in medium devoid of lipoproteins. 14C-oleic acid incorporation into cholesteryl-esters was 2 to 3 fold reduced in NPC cells, and esterification of 14C-exogenous cholesterol was dramatically (15-30 fold) decreased. ACAT activity, measured in vitro, was not significantly altered in NPC cells. Finally, cholesterol efflux appeared to be decreased in NPC fibroblasts as compared to controls. The hypothesis of a defect in exogenous cholesterol access to intracellular regulatory pools is proposed.

Cells, Cultured↗
PubMed1986

[Development of esterification capacity of fatty acids in the adipocytes of the rat before weaning: the effect of milk overfeeding].

During the suckling period, lipid storage in rat adipose tissue arises from exogenous triglycerides, as milk contains a large amount of lipid. In the present work, we studied the effect of overfeeding during the suckling period on the developmental pattern of the fatty acid esterification pathway in fat cells. Early overfeeding was induced by restricting litter size; at 2 days of age, the pups were randomly distributed to form litters of 4 (overfed group) or 8 (controls). During the suckling period the activity of lipoprotein lipase (LPL), glycerophosphate dehydrogenase (G3PDH), glycerophosphate acyl transferase (GPAT) and acyl CoA ligase were measured in isolated fat cells from the inguinal adipose tissue. As early as 10 days of age, plasma triglyceride levels were increased in overfed pups as compared to the controls and, in these animals, the adipose tissue was overdeveloped, mainly due to fat cell hypertrophy. At that age, overfeeding induced a significant increase in LPL and GPAT activities, but acyl CoA ligase and GPDH were not modified in overfed pups. Fat cell hypertrophy appeared to be responsible for the increased GPAT activity in the overfed pups. On the contrary, the effect of overfeeding on LPL activity was not only related to fat cell enlargement, as the enzyme activity continued to increase in the overfed rats when expressed per unit of cell surface area. These results show that overfeeding during the suckling period rapidly induced an increase in the fat storage capacity of the adipose tissue. This suggests that circulating triglyceride levels could regulate directly or through hormonal control the activity of the fatty acid esterification pathway in fat cells.

Adipose Tissue↗
PubMed1982

Esterification of the carboxyl groups in fibrinogen by the application of a highly specific methylating agent.

The trimethyl oxonium ion specifically modified the free carboxyl groups of fibrinogen. This esterification process resulted in the polymerization of the modified fibrinogen molecule with the production of a polymeric material that resembled the physiologically formed fibrin clot. The extent of methylation of fibrinogen was evaluated by methoxyl determination at each step of the polymerization process. The modified fibrinogen polymerized in approximately ten min with a minimum number of methyl groups being incorporated into the fibrinogen molecule. In this manner, it was shown that modification of carboxyl groups in the fibrinogen by a group-specific methylating agent results in polymerization of fibrinogen. The sites of methylation were ascertained by chromatographic analysis which resulted in the identification of beta-methyl aspartic acid and gamma-methyl glutamic acid derivatives of the fibrinogen. The analytical methods applied were not able to detect the methylation of any additional amino acid residues in the polymerized-methylated fibrinogen. Based on this experimental data, it was formulated that the methylation of fibrinogen involved the esterification of the carboxyl groups of aspartic and glutamic acid with the resultant reduction of negative repulsion between the fibrinogen molecules and thereby culminated in the polymerization of the modified fibrinogen.

Animals↗
PubMed1984

Interactions between fatty acid synthesis, oxidation, and esterification in the production of triglyceride-rich lipoproteins by the liver.

In a series of experiments with male rat livers perfused with or without 5-tetradecyloxy-2-furoic acid (TOFA) in the presence and absence of oleate, the relationships between fatty acid synthesis, oxidation, and esterification from newly synthesized and exogenous fatty acid substrates have been examined. When livers from fed rats were perfused without exogenous fatty acid substrate, 20% of the triglyceride secreted was derived from de novo fatty acid synthesis. Addition of TOFA caused immediate and nearly complete inhibition of fatty acid synthesis, measured by incorporation of 3H2O into fatty acids. Concurrently, ketone body production increased 140% and triglyceride secretion decreased 84%. These marked reciprocal alterations in fatty acid synthesis and oxidation in the liver almost completely abolished the production of very low density lipoproteins (VLDL). Cholesterol synthesis was also depressed by TOFA, suggesting that this drug also inhibited lipid synthesis at a site other than acetyl-CoA carboxylase. When livers from fed rats were supplied with a continuous infusion of [1-14C]oleate as exogenous substrate, similar proportions, about 45-47%, of both ketone bodies and triglyceride in the perfusate were derived from the infused [1-14C]oleate. The production of ketone bodies was markedly increased by TOFA; the secretion of triglyceride and cholesterol were decreased. Altered conversion of [1-14C]oleate into these products occurred in parallel. While TOFA decreased esterification of oleate into triglyceride, incorporation of [1-14C]oleate into liver phospholipid was increased, indicating that TOFA also affected glycerolipid synthesis at the stage of diglyceride processing. The decreased secretion of triglyceride and cholesterol following TOFA treatment was localized almost exclusively in VLDL. The specific activities of 3H and of 14C fatty acids in triglyceride of the perfusate were greater than those of liver triglyceride, indicating preferential secretion of triglyceride produced from both de novo fatty acid synthesis and from infused free fatty acid substrate. These observations suggest the following chain of events in the liver following TOFA treatment: inhibition of fatty acid and cholesterol synthesis; increased fatty acid oxidation and ketogenesis; decreased triglyceride synthesis as a result of inhibition of fatty acid synthesis, stimulation of fatty acid oxidation, and altered partition of diglyceride between triglyceride and phospholipid synthesis; and decreased production of VLDL. These comparative rat liver perfusion experiments indicate that free fatty acids provide the major source of substrate for the hepatic production of triglyceri

Animals↗
PubMed1981

The effect of pancreatic diversion on lymphatic absorption and esterification of cholesterol in the rat.

Lymph fistula rats with either biliary fistula or pancreaticobiliary fistula were used to measure coenzyme A-independent mucosal cholesterol esterifying activity in the presence and absence of pancreatic exocrine secretion. Efficiency of pancreatic diversion was verified to minimize contamination of mucosal homogenates with adherent luminal enzyme. The synthetic activity of cholesteryl ester hydrolase (E.C. 3.1.1.13) was measured directly in mucosal homogenates. Indirect evidence for mucosal esterifying activity was obtained from hourly cholesteryl ester output into lymph when other factors known to affect cholesterol absorption were controlled. Rats infused intraduodenally at a constant rate with different concentrations of bile salts, polar lipid, and [3H]cholesterol showed that the infused [3H]cholesterol was absorbed and esterified with equal efficiency in the presence and absence of pancreatic flow. Total lymph output of free and esterified endogenous cholesterol was slightly less efficient in the pancreaticobiliary fistula group (85% of bile fistula values) but percent esterification was the same for both groups. Infusion of lipid-free micellar bile salts separately from other bile components produced a highly significant increase in absorption and esterification of lymph cholesterol for both groups. No correlation was found between cholesterol esterifying activity in a) the lumen or b) the mucosa, and cholesteryl ester output into lymph. The present study suggests an alternative enzyme dependent directly or indirectly on the presence of micellar bile salts in the lumen to explain intestinal cholesterol esterifying activity during absorption.

Acyltransferases↗
PubMed1980

Initial rate of cholesterol esterification association with high density lipoproteins in human plasma.

The enzyme lecithin:cholesterol acyl transferase has been measured both in total plasma and in the fraction of plasma from which very low and low density lipoproteins have been removed by ultracentrifugation. The correlation between the activity of the enzyme and the free cholesterol concentration was positive in whole plasma and negative in apoB-deficient plasma. On the other hand, the positive correlation between plasma triglycerides and cholesterol esterification was not changed by the removal of apoB-containing lipoproteins. Subjects with the highest levels of high density lipoprotein cholesterol were found to have the lowest enzyme activity, but this correlation was disclosed only in apoB-deficient plasma. This inverse relationship was abolished when the enzyme activity was measured in the absence of all lipoproteins with a density less than 1.125 g/ml. Cholesterol esterification, when determined after removal of lipoproteins with a density less than 1.063 g/ml, was negatively correlated with the in vivo plasma concentration of lipoproteins in the density range 1.063-1.125 g/ml. The same results were obtained in vitro by addition of increasing amounts of this class of high density lipoproteins either in total plasma or in the ultracentrifuged fractions of plasma. This provides further evidence that the lighter density class of high density lipoproteins inhibits the enzyme reaction under physiological conditions.

Adult↗
PubMed1993

Elongation, desaturation, and esterification of essential fatty acids by fetal rat brain in vivo.

Tracer amounts of either [1-14C]linolenic (18:3n-3, LNA), or [1-14C]linoleic (18:2n-6, LA) acids were intracranially injected into 19- to 20-day-old rat fetuses, and the time course of the in vivo formation and esterification of their long chain polyenoic metabolites was determined for up to 20 h. A rapid disappearance of free LNA and LA, with apparent half-lives of 60 and 40 min, respectively, was noticed. One hour after LNA injection, 32.3% and 14.3% of the total brain radioactivity was found in the neutral glyceride (NG) and phospholipid (PL) fractions, respectively. After 20 h, PL radioactivity attained a level of 75%. Phosphatidylcholine (PC), diacylglycerol (DG), and triacylglycerol (TG) constituted 40%, 23%, and 9% of the total brain label at 1 h, and 35%, 10% and 14% at 20 h, respectively. Ethanolamine-containing PL (including plasmalogen) radioactivity accounted for about 10% up to 6 h and increased nearly 3-fold at 20 h, primarily due to an increase in the amount of labeled docosapentaenoic and docosahexaenoic acids (DHA), the elongation-desaturation products of LNA. A similar pattern of incorporation into NG and PL fraction was observed after the administration of [1-14C]LA. After 1 h, PC, DG, and TG species constituted 23%, 10%, and 23% of the total brain radioactivity, whereas after 20 h it accounted for 44%, 6%, and 10%, respectively. Although radioactivity in the ethanolamine PL also increased substantially from 4% at 1 h to 29% at 20 h, the main labeled fatty acid in this fraction was LA. Labeled arachidonic acid (AA) constituted 42.7% of the total radioactivity in phosphatidylinositol (PI) at 20 h. At this time, it comprised 12.5% and 14% of the total radioactivity in PC and ethanolamine PL, respectively, suggesting a high degree of esterification selectivity. Comparison of the total amounts of LA and LNA and their corresponding labeled AA and DHA metabolites in brain and liver after 3 and 6 h indicated that the contribution of liver metabolism to the elongation-desaturation under these conditions was negligible. One hour after intracerebral injection of [3H]DHA (22:6n-3) or [3H]AA (20:4n-6), 29.2% and 12% of total radioactivity, respectively, was found in the ethanolamine PL while 20% and 40% was incorporated in PC, respectively. PI labeling by [3H]AA was 6- to 8-fold higher than that seen in the presence of DHA. A high percent of radioactivity (26.9% and 18.2%) was found in DG and TG species.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetyltransferases↗
PubMed1993

Catalysis of the hydrolysis of ethyl mandelate and esterification of alpha-bromopropionic acid by lipase in microemulsions.

Candida cyclindracea lipase (CCL) was added to "sodium dodecyl sulfonate (AS)/n-butanol/n-octane/n-octane" water-in-oil microemulsion to catalyze the hydrolysis of ethyl mandelate and the esterification of alpha-bromopropionic acid with n-butanol, respectively. The catalytic activity of CCL in the above microemulsions was higher than that in the traditional oil/water biphasic systems. After hydrolysis for 48 h, the conversion rate of the reaction reached 90% and S-mandelic acid, [alpha]D20-149.8 (C10; H2O), optical purity ca. 97%, was isolated. While after esterification for 6 h, the conversion rate of the reaction reached 45%, and butyl-(R)-alpha-bromopropionate, [alpha]D20 18.2 (Cl; CHCl3), optical purity ca. 99%, was obtained.

1-Butanol↗
PubMed1997

Comparison of acid anhydrides with carboxylic acids in enantioselective enzymatic esterification of racemic menthol.

Optical resolution of racemic menthol has been efficiently achieved by lipase-catalyzed enantioselective esterification in an organic solvent. The performance of the reaction using an acid anhydride as an acyl donor was compared with that using its corresponding free acid. The reactivities of acid anhydrides were found to be higher than their corresponding free acids, but acid anhydrides were also found to be easily hydrolyzed into free acids under the catalysis of the same enzyme. The existence of a too-high concentration of an acid anhydride in a micro-aqueous reaction system will cause dehydration and thus deactivation of the enzyme, and will enhance non-selective esterification of a chiral alcohol, which will reduce the optical purity of the product. All these drawbacks, however, could be effectively overcome in a semi-batch reaction system into which propionic anhydride was continuously fed. This system showed some advantages over a batch reaction system using free propionic acid: the reaction time of dl-menthol was shortened by half, the stability of the enzyme was much enhanced, and the optical purity of the product (l-menthyl ester) was kept at a similarly high level (> 98% ee).

Acids↗
PubMed2000

Continuous enzymatic esterification of glycerol with (poly)unsaturated fatty acids in a packed-bed reactor.

Enzymatic synthesis of mono-, di-, and triacyglycerols from (poly)unsaturated fatty acids (linoleic, oleic, and conjugated linoleic acids) has been studied as a solvent-free reaction in a packed-bed reactor containing an immobilized lipase from Mucor miehei. The extents of the esterification reactions of interest are primarily determined by the molar ratio of glycerol to fatty acid because the presence of excess glycerol as a immiscible phase is responsible for reducing the activity of the water produced by the esterification reactions. For molar ratios of fatty acid to glycerol of less than 1.5, the percentage of the fatty acid esterified decreases quasi-linearly with an increase in this molar ratio. By appropriate manipulation of the fluid-residence time, one can control the relative proportions of the various acylglycerols in the effluent stream. At the outlet of the reactor, one observes excellent spontaneous separation of the glycerol and acylglycerol/fatty acid phases. At 50 degrees C and a fluid residence time of 1 hour, as much as 90% of the fatty acid can be esterified when the molar ratio of fatty acid to glycerol is 0.33 or less.

Bioreactors↗
PubMed1996

Co-cultivation of Niemann-Pick disease type C fibroblasts belonging to complementation groups alpha and beta stimulates LDL-derived cholesterol esterification.

Niemann-Pick disease type C (NPC) is a neurovisceral storage disorder with an unknown primary deficiency. Somatic cell hybridization experiments using human cultured fibroblasts have shown that two complementation groups (NPC-alpha and NPC-beta) are associated with the biochemical and clinical phenotypes comprising NPC. We identified the rarer complementation group NPC-beta originally using the technique of filipin staining as a marker for complementation. In this study we show that the esterification of cholesterol derived from the LDL pathway can be used as an isotopic assay. However, multinuclear hybrids exhibit a delayed induction in this pathway. Furthermore, we discovered that, in the presence of an LDL source, co-cultivation of fibroblasts belonging to NPC-alpha and NPC-beta stimulated cholesterol esterification.

Cholesterol↗
PubMed1997

An esterification protocol for cis-parinaric acid-determined lipid peroxidation in immune cells.

Loss of fluorescence from cis-parinaric acid (cPnA) is a sensitive indicator of lipid peroxidation. The purpose of this study was to utilize cPnA to determine, at the level of the intact immune cell, whether enrichment of membranes with polyunsaturated fatty acids (PUFA) increased lipid peroxidation. P388D1 macrophages were labeled by addition of cPnA as an ethanolic solution. Within two minutes of addition, in the absence-of serum, cPnA rapidly intercalated into the plasma membrane. Lipid peroxidation was initiated by addition of Fe(2+)-EDTA resulting in a dose-dependent decrease in fluorescence with increased oxidant concentration. Cells previously enriched with PUFA and labeled by intercalation showed no differences in spontaneous or Fe(2+)-induced lipid peroxidation. In separate experiments, 20 microM cPnA in ethanolic solution was injected into cell culture media containing 0.1% essentially fatty acid free bovine serum albumin (BSA). Cells were resuspended and incubated for 90 min at 37 degrees C. After washing with BSA to remove cPnA which had not incorporated, 0.5% (0.1 microM) of the added cPnA was found esterified within cellular lipids. This level of cPnA provided a 100-fold increase over basal autofluorescence levels. Cells labeled in this manner also lost fluorescence in a dose-dependent manner as levels of oxidant stress increased. Cells enriched with PUFA and labeled by esterification had significantly increased rates and total amounts of lipid peroxidation. Co-incubation with alpha-tocopherol and PUFA resulted in a decrease in lipid peroxidation which was not significantly different from control cells. In conclusion, esterification of cPnA into membrane phospholipids can sensitively detect changes in lipid peroxidation induced by alteration of membrane PUFA and/or vitamin E content.

Cells, Cultured↗
PubMed1995

Lipase catalyzed esterification in AOT reverse micelles: a structural study.

AOT reverse micelles are used to cosolubilize hydrophilic and hydrophobic reactants of lipase catalysed esterification. Depending on the nature of the alcohol, a drastic change of the initial rate of the esterification is observed. A structural study of the micellar system with and without reactant is undertaken to explain the change in the activity with the various alcohols.

Catalysis↗
PubMed1975

Genetic control of sterol esterification in developing wheat endosperm.

1. The action of gene Pln, previously characterized by the sterol ester patterns of mature whole wheat kernels, has been found to be restricted to the endosperm and not to affect the embryo, the pericarp or the seed coat. 2. The dominant allele Pln, which determines a sterol ester pattern with palmitate as the main ester, is also responsible for a low level of free sterol at maturity. A high level of free sterol is associated with the recessive allelet pln, which determines an ester pattern with linoleate as the main ester. 3. Divergence between the two phenotypes starts at about 21 days after anthesis, when cell proliferation has been completed, the aleurone layer has differentiated, and only cell enlargement is taking place. A marked increased in esterification, mainly by palmitate, which is controlled by the dominant allele, is concomitant with a sharp decrease in free sterol. 4. The increased net esterification is non-specific with respect to 4-demethyl sterols, because it affects the four main ones, namely sitosterol, stigmasterol, campesterol and cholesterol.

Alleles↗
PubMed1985

Reciprocal effects of energy utilization on palmitate oxidation and esterification in hepatocytes of fed rats.

The effects of the energy-dependent process of urea synthesis from NH4Cl on the partition of [1-14C]palmitate between oxidation and esterification were examined in hepatocytes of fed rats. A high rate of urea formation from NH4Cl resulted in stimulation of total palmitate oxidation by 25 and 15% at 0.2 and 1 mM fatty acid, respectively. The stimulation of palmitate oxidation was reciprocally correlated with diminished palmitate incorporation into lipids, mainly triacylglycerols. This relationship was almost stoichiometric. NH4Cl increased the palmitate oxidation/esterification ratio from 0.72 to 1.13 and from 0.94 to 1.36 in the presence of 0.2 mM and 1 mM palmitate, respectively. The transaminase inhibitor, aminooxyacetate, strongly inhibited urea synthesis from NH4Cl, had little effect on the low beta-hydroxybutyrate/acetoacetate ratio in the presence of NH4Cl, completely reversed the changes in palmitate metabolism caused by NH4Cl and did not affect palmitate metabolism in the absence of NH4Cl. Therefore, the increased utilization of energy for urea synthesis was the causative factor by which NH4Cl stimulated total palmitate oxidation and led in consequence to its decreased esterification into lipids. Accordingly, these observations indicate that in liver cells the rate of ATP utilization is one of the determinants of triacylglycerol synthesis.

Aminooxyacetic Acid↗
PubMed1987

Impaired cholesterol esterification in primary brain cultures of the lysosomal cholesterol storage disorder (LCSD) mouse mutant.

Esterification of cholesterol was investigated in primary neuroglial cultures obtained from newborn lysosomal cholesterol storage disorder (LCSD) mouse mutants. An impairment in 3H-oleic acid incorporation into cholesteryl esters was demonstrated in cultures of homozygous LCSD brain. Primary cultures derived from other phenotypically normal pups of the carrier breeders esterified cholesterol at normal levels or at levels which were intermediary between normal and deficient indicating a phenotypic expression of the LCSD heterozygote genotype. These observations on LCSD mutant brain cells indicate that the defect in cholesterol esterification is closely related to the primary genetic defect and is expressed in neuroglial cells in culture.

Animals↗
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↗