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At least 163 records · Page 9Linked to original sources
PubMed1993

Role of sphingomyelin in the regulation of cholesterol esterification in the plasma lipoproteins. Inhibition of lecithin-cholesterol acyltransferase reaction.

In order to determine whether sphingomyelin (SPH) affects the rate of cholesterol esterification by plasma lecithin-cholesterol acyltransferase (LCAT), we studied the effects of its incorporation in to defined proteoliposome substrates containing phosphatidyl choline (PC), unesterified cholesterol, and apoprotein A-I, on the activity of purified LCAT. Cholesterol esterification was inhibited by up to 90% in the presence of SPH, and this inhibition was reversed by treatment with bacterial sphingomyelinase. The inhibition could be overcome by increasing the concentration of PC, but not unesterified cholesterol or apoprotein A-I, in the substrate. The effect of SPH was not related to the alterations in the size of the substrate particle and was not dependent on the type of acyl donor or apoprotein activator employed. The lysolecithin acyltransferase and phospholipase reactions carried out by LCAT were also inhibited by SPH. Kinetic studies suggested that: 1) LCAT binds better to substrate vesicles which contain SPH; 2) SPH competes with PC in binding to the active site of the enzyme; and 3) SPH is a more powerful competitive inhibitor than a diether analog of PC. The ability of various lipoproteins to act as substrates for purified LCAT varied inversely with the SPH/PC ratio. Treatment of the lipoproteins with sphingomyelinase activated the LCAT reaction, the percent activation being directly proportional to the SPH concentration in the native lipoprotein. Enrichment of high density lipoproteins with SPH inhibited cholesterol esterification in them by 50%, and this inhibition could be reversed by the degradation of SPH. These results show that SPH is a physiological inhibitor of cholesterol esterification in the plasma, by virtue of its competition with PC, the acyl donor for the reaction.

Apolipoprotein A-I↗
PubMed1997

A conditional sterol esterification defect in yeast having either a sec1 or sec5 mutation in the secretory pathway.

Two temperature-conditional secretory mutations, sec1 and sec5, cause the accumulation of post-Golgi vesicles when strains containing these mutations are grown at 37 degrees C. In addition to accumulating vesicles, the mutants do not esterify free sterol on rich media at the restrictive temperature. It is the high level of inositol in the media that causes this condition in the yeast Saccharomyces cerevisiae, not a defective steryl ester synthase or lack of substrates. When strains containing the sec1 or sec5 mutation were transformed separately with a plasmid carrying SEC1 and SEC5, the esterification and secretory defects were alleviated. Double mutants containing sec6, sec14 or sec18 with either a sec1 or sec5 mutation have normal esterification levels. Strains with suppressor mutations were isolated that grew at 37 degrees C, esterified sterols and had diminished accumulation of vesicles, when grown at the restrictive temperature on defined media with additional inositol. Electron microscopy was used to examine vesicle accumulation, the number of lipid droplets, and to further characterize the esterification defect. When grown at 37 degrees C on defined medium, the strains with sec5 or sec1 accumulated the usual secretory vesicles, but when grown under similar conditions with elevated levels of inositol, accumulated an additional vesicular-like body.

Esterification↗
PubMed2002

Synthesis of phosphatidylcholine with defined fatty acid in the sn-1 position by lipase-catalyzed esterification and transesterification reaction.

The incorporation of caproic acid in the sn-1 position of phosphatidylcholine (PC) catalyzed by lipase from Rhizopus oryzae was investigated in a water activity-controlled organic medium. The reaction was carried out either as esterification or transesterification. A comparison between these two reaction modes was made with regard to product yield, product purity, reaction time, and byproduct formation as a consequence of acyl migration. The yield in the esterification and transesterification reaction was the same under identical conditions. The highest yield (78%) was obtained at a water activity (a(w)) of 0.11 and a caproic acid concentration of 0.8 M. The reaction time was shorter in the esterification reaction than in the transesterification reaction. The difference in reaction time was especially pronounced at low water activities and high fatty acid concentrations. The loss in yield due to acyl migration and consequent enzymatic side reactions was around 16% under a wide range of conditions. The incorporation of a fatty acid in the sn-1 position of PC proved to be thermodynamically much more favorable than the incorporation of a fatty acid in the sn-2 position.

Catalysis↗
PubMed2004

Polymer-bound alkyltriazenes for mild racemization-free esterification of amino acid and peptide derivatives.

A novel tool for polymer-assisted solution phase (PASP) esterification of amino acid and peptide derivatives has been developed. When treated with carboxylic acids, polymer-bound alkyltriazenes react with a loss of nitrogen and transfer of the alkyl moiety to the carboxylate anion to form the corresponding alkyl esters. There are no limitations with regard to either the protecting groups or the nature of the amino acid. Furthermore no racemization occurs at the chiral centers of the amino acids as demonstrated by chiral GC-MS analyses. Alkyltriazene-resins were also applied successfully to the esterification of peptide acids and other peptidic structures, such as tripalmitoyl-S-glyceryl-cysteine (Pam3Cys). The triazene-mediated esterification reaction is exceptionally mild, and there is no need for prior activation of the carboxy groups. This method is therefore particularly suitable for the alkylation of complex peptidomimetic structures prone to racemization and for acid-sensitive structures.

Amino Acids↗
PubMed2003

Fatty acid esterification in the yolk sac membrane of the avian embryo.

The transfer of lipid from the yolk to the avian embryo is mediated by the yolk sac membrane (YSM). Some, but not all, of the published morphological evidence supports the view that the lipid undergoes a cycle of hydrolysis and re-esterification during translocation across the YSM. The present study aims to test this view by investigating the capacity of the YSM to perform esterification of free fatty acids to form acyl-lipids. YSM pieces (area vasculosa), obtained from the chicken embryo at day 10 of development, were incubated in vitro in medium containing [14C]-palmitic acid. Radioactivity was rapidly incorporated into the tissue lipid indicating a high capacity for esterification. The incorporation was linear with time during the 1-h incubation. Approximately 84% of the incorporated label was recovered in triacylglycerol, 12% was incorporated into phospholipid and less than 1% was detected in cholesteryl ester. [14C]-palmitic acid was incorporated primarily at the sn-1/3 positions in the triacylglycerol molecule and at the sn-1 position of phospholipid. The incorporation of label into tissue pieces obtained from the non-vascularized peripheral region of the YSM (area vitellina) was much more limited than that observed for the area vasculosa. The results support the hypothesis that yolk lipid is hydrolyzed and re-esterified during transfer across the YSM.

Animals↗
PubMed2006

Deficiency of adenosine kinase activity affects the degree of pectin methyl-esterification in cell walls of Arabidopsis thaliana.

Pectin methyl-esterification is catalysed by S-adenosyl-L: -methionine (SAM)-dependent methyltransferases. As deficiency in adenosine kinase (ADK; EC 2.7.1.20) activity impairs SAM recycling and utilization, we investigated the relationship between ADK-deficiency and the degree of pectin methyl-esterification in cell walls of Arabidopsis thaliana. The distribution patterns of epitopes associated with methyl-esterified homogalacturonan in leaves and hypocotyls of wild-type (WT) and ADK-deficient plants were examined using immunolocalization and biochemical techniques. JIM5 and LM7 epitopes, characteristic of low esterified pectins, were more irregularly distributed along the cell wall in ADK-deficient plants than in WT cell walls. In addition, epitopes recognized by JIM7, characteristic of pectins with a higher degree of methyl-esterification, were less abundant in ADK-deficient leaves and hypocotyls. Since de-esterified pectins have enhanced adhesion properties, we propose that the higher abundance and the altered distribution of low methyl-esterified pectin in ADK-deficient cell walls lead to the leaf shape abnormalities observed in these plants.

Adenosine Kinase↗
PubMed2000

Esterification of polyunsaturated fatty acids by various forms of immobilized lipase from Rhizomucor miehei.

Ethyl esterification specificity of a lipase from Rhizomucor miehei for polyunsaturated fatty acids (PUFA) was compared at 1 and 100 mM to study molecular recognition of PUFA. The chemical shift of methylene adjacent to carboxyl groups in the nuclear magnetic resonance spectrum of docosahexaenoic acid (DHA) in ethanol moved to a lower magnetic field as the concentration of DHA increased, suggesting that the degree of dissociation of DHA decreased. Specificity constants or apparent second-order rate constants (Vmax/Km or catalytic power) for 1 mM esterification by immobilized lipases were higher than the native lipase. Immobilized hydrophobic carrier of low mass transfer resistance for the esterification substrate may improve maximal velocity and affinity for the substrate. Higher specificity constants for 1 mM substrates were observed using immobilized lipases fixed on an anion exchange resin with glutaraldehyde and on a cation exchange carrier with carbodiimide. Activity yields measured with 1 mM PUFA substrate were high. For the substrates at a concentration of 100 mM, higher specific constants with these bifunctional reagents were not observed but higher activity yields were found.

Anions↗
PubMed1990

Determination of the degree of methyl esterification of pectins in small samples by selective reduction of esterified galacturonic acid to galactose.

A procedure for the determination of the degree of methyl esterification of pectin in virtually any sample is described. Samples were dissolved or suspended in 1 M imidazole buffer, pH 7.0, cooled on ice, and reduced with sodium borohydride. Quantitative reduction of samples was accomplished after 1 h using at least 20 mg sodium borohydride/mg sample. The degree of methyl esterification was determined by either the increase in galactose content as determined by GLC of the sugar or by the change in galacturonic acid content by colorimetric uronic acid analyses. Sample requirements were at least as low as 100 micrograms per determination by GLC or 2 to 3 mg per determination by colorimetric uronic acid analysis compared to 5 mg or more per determination for other published procedures. The degrees of methyl esterification determined by the methods described have compared very favorably with those determined by established methods.

Chromatography, Gas↗
PubMed1991

Regio- and stereoselective enzymatic esterification of glycerol and its derivatives.

A methodology for regio- and stereoselective preparation of acyl glycerol derivatives is presented. It offers easy access to specific 1,2-, 1,3-diglycerides and triglycerides as well as alkyl glycerol esters, phospholipids and glycolipids. These compounds are prepared by esterification of the corresponding glycerol derivatives such as 2-monoglycerides, alkyl glycerols, glyceryl glycosides, glyceryl phosphate esters, or unsubstituted glycerol. The regio- and stereoselectivity in the esterification is achieved by using fatty acid anhydrides and an enzymatic catalyst, 1,3-specific lipase. NMR methods for determining the regio- and stereoselectivity of esterification are discussed.

Esterification↗
PubMedDate not supplied

The effect of local anesthetics on arterial lipid metabolism. Inhibition of sterol esterification in vitro.

The local anesthetics lidocaine, tetracaine, benzocaine and dibucaine were found to inhibit sterol esterification by acylCoA:cholesterol acyltransferase (ACAT, EC 2.3.1.26) in the microsomal fraction isolated from rabbit aortas. In arterial microsomes, the incorporation of [14C]oleoylCoA into [14C]steryl esters was inhibited in a dose-dependent way by the anesthetics over the concentration range 0.25-5.0 mM. The potency of inhibition was dibucaine greater than benzocaine greater than tetracaine greater than lidocaine greater than procaine with inhibition of about 85% occurring with 0.25 mM dibucaine. Sterol esterification to [14C]oleic acid was also inhibited by the anesthetics in intact aortic tissue from the rabbit, dog, and rat. A detailed study of the effects of 5 mM lidocaine on lipid biosynthesis in the rabbit aorta in vitro revealed that lidocaine not only inhibited sterol esterification to [14C]oleate but stimulated [14C]oleate incorporation into glycerides.

Anesthetics↗
PubMed1984

Induction of retinol esterification in retinal pigment epithelial cells by butyrate.

Butyrate induced marked morphological changes in cultured human retinal pigment epithelial (RPE) cells. The cells assumed a flattened structure within six hours of exposure to butyrate. The butyrate-treated retinal pigment epithelial cells possessed an enhanced capacity to esterify retinol. Among all short chain organic acids tested, butyrate was by far the most effective, followed by pentanoate and hexanoate. The inductive effect of butyrate was specific for retinol esterification, since the incorporations of fatty acid into phosphatidyl choline and cholesteryl ester were not enhanced. Time-dependent, butyrate-enhanced retinol esterification may be related to the inhibition of cell proliferation. This represents the first report on the induction of retinol esterification in cultured retinal pigment epithelial cells.

Adolescent↗
PubMed2006

Enzymatic esterification of starch using recovered coconut oil.

Modification of maize and cassava starches was done using recovered coconut oil and microbial lipase. Microwave esterification was advantageous as it gave a DS 1.55 and 1.1 for maize starch and cassava starch, respectively. Solution state esterification of cassava starch for 36 h at 60 degrees C gave a DS of 0.08 and semi-solid state esterification gave a DS of 0.43. TGA and DSC studies showed that the higher DS attributed to the thermostability, since onset of decomposition is at a higher temperature (492 degrees C) than the unmodified (330 degrees C) and was stable above 600 degrees C. alpha-Amylase digestibility and viscosity reduced for modified starch.

Calorimetry, Differential Scanning↗
PubMed2004

Enzymatic esterification of beta-methylglucoside with acrylic/methacrylic acid in organic solvents.

The enzymatic esterifications of beta-methylglucoside with acrylic acid/methacrylic acid were carried out using Novozym 435. t-Butanol indicating the highest conversion value was determined as an optimal solvent. The molar ratio (beta-methylglucoside:acids) of 1:15 was most favorable to the esterification. The enzyme concentration of 5% (w/v), and the temperature (50 degrees C for beta-methylglucoside:acrylic acid, 45 degrees C for beta-methylglucoside:methacrylic acid) resulted in the highest final conversion. Beta-methylglucoside of 60gl(-1) was found to be most effective in terms of short reaction time as well as product concentrations. Under these conditions, the maximum conversions for the esterification of beta-methylglucoside with acrylic acid and beta-methylglucoside with methacrylic acid were 59.3% after 12h and 71.3% after 72h, respectively. The structural analysis of the products was performed by FT-IR spectroscopy and (1)H NMR.

Acrylates↗
PubMed2004

Esterification of vertebrate-type steroids in the Eastern oyster (Crassostrea virginica).

Characteristics of acyl-coenzyme A (acyl-CoA):steroid acyltransferase from the digestive gland of the oyster Crassostrea virginica were determined by using estradiol (E2) and dehydroepiandrosterone (DHEA) as substrates. The apparent Km and Vmax values for esterification of E2 with the six fatty acid acyl-CoAs tested (C20:4, C18:2, C18:1, C16:1, C18:0, and C16:0) were in the range of 9-17 microM E2 and 35-74 pmol/min/mg protein, respectively. Kinetic parameters for esterification of DHEA (Km: 45-120 microM; Vmax: 30-182 pmol/min/mg protein) showed a lower affinity of the enzyme for this steroid. Formation of endogenous fatty acid esters of steroids by microsomes of digestive gland and gonads incubated in the presence of ATP and CoA was assessed, and at least seven E2 fatty acid esters and five DHEA fatty acid esters were observed. Some peaks eluted at the same retention times as palmitoleoyl-, linoleoyl-, oleoyl/palmitoyl-, and stearoyl-E2; and palmitoleoyl-, oleoyl/palmitoyl-, and stearoyl-DHEA. The same endogenous esters, although in different proportions, were produced by gonadal microsomes. The kinetic parameters for both E2 (Km: 10 microM; Vmax: 38 pmol/min/mg protein) and DHEA (Km: 61 microM; Vmax: 60 pmol/min/mg protein) were similar to those obtained in the digestive gland. Kinetic parameters obtained are similar to those observed in mammals; thus, fatty acid esterification of sex steroids appears to be a well-conserved conjugation pathway during evolution.

Acyltransferases↗
PubMed2001

Continuous enantioselective esterification of trans-2-phenyl-1-cyclohexanol using a new Candida rugosa lipase in a packed bed bioreactor.

Enantioselective resolution of trans-2-phenyl-1-cyclohexanol (TPCH) by a Candida rugosa lipase, obtained by fermentation in the laboratory, and immobilised on EP100 polypropylene powder has been carried out using isooctane as solvent and propionic acid as esterifying agent. The study have included the utilisation of this biocatalyst in a batch process and the optimisation of the esterification conditions by means of a Box-Hunter-based experimental design. The main variables controlling the process, concentration of acid and alcohol, have been numerically optimised using initial esterification rate as objective function. The optimal concentrations for the batch process were 50 mM for the alcohol and 71 mM for the acid. This esterification reaction kinetics corresponded to a reversible Michaelis-Menten kinetic law for the optimal conditions, which has permitted to select a plug-flow packed bed bioreactor as the most appropriate configuration to minimise the residence time and to avoid shear stress effect on the biocatalyst. The behaviour of the continuous packed bed bioreactor at two different residence times (302 and 582 min) was in accordance with predictions from batch experiments, with slightly deviations (less than 10%). Continuous experiments maintained high values of enantioselectivity (enantiomeric factor was practically 1) and conversion near equilibrium value (35%) when long-time operation was carried out. Besides, long-time stability of biocatalyst has permitted to scale-up the production of enantioenriched (1R,2S)-TPCH propionate to yield gram quantities.

Bioreactors↗
PubMed2001

Fatty acid steryl, stanyl, and steroid esters by esterification and transesterification in vacuo using Candida rugosa lipase as catalyst.

Sterols (sitosterol, cholesterol, stigmasterol, ergosterol, and 7-dehydrocholesterol) and sitostanol have been converted in high to near-quantitative yields to the corresponding long-chain acyl esters via esterification with fatty acids or transesterification with methyl esters of fatty acids or triacylglycerols using lipase from Candida rugosa as biocatalyst in vacuo (20-40 mbar) at 40 degrees C. Neither organic solvent nor water is added in these reactions. Under similar conditions, cholesterol has been converted to cholesteryl butyrate and steroids (5alpha-pregnan-3beta-ol-20-one or 5-pregnen-3beta-ol-20-one) have been converted to their propionic acid esters, both in moderate to high yields, via transesterification with tributyrin and tripropionin, respectively. Reaction parameters studied in esterification include the temperature and the molar ratio of the substrates as well as the amount and reuse properties of the C. rugosa lipase. Lipases from porcine pancreas, Rhizopus arrhizus, and Chromobacterium viscosum are quite ineffective as biocatalysts for the esterification of cholesterol with oleic acid under the above conditions.

Candida↗
PubMed1984

Uptake and esterification of exogenous cholesterol by low-density-lipoprotein-receptor-negative human fibroblasts in culture.

The incorporation and metabolism of both vesicle- and LDL (low-density lipoprotein)- derived [3H]cholesterol by LDL-receptor-negative fibroblasts were studied. Independent of the cholesterol source, free [3H]cholesterol was readily incorporated into the cells and was available for esterification. 7-Oxocholesterol stimulated both [3H]cholesterol incorporation, by increasing the exchange rate, and the subsequent esterification of it irrespective of the source of exogenous [3H]cholesterol. The 7-oxocholesterol-stimulated esterification of exogenously derived LDL free [3H]cholesterol was progesterone-sensitive and energy-requiring.

Cell Line↗
PubMed1995

Insulin-independent and extremely rapid switch in the partitioning of hepatic fatty acids from oxidation to esterification in starved-refed diabetic rats. Possible roles for changes in cell pH and volume.

The requirement for a normal insulin response in mediating the starved-to-refed transition, with respect to the partitioning of hepatic fatty acids between beta-oxidation and esterification to glycerol, was studied. Diabetic rats were starved for 24 h and refed ad libitum for various periods of time. There was no increase in plasma insulin in response to the meal. However, the fatty acid oxidation:esterification ratio was very rapidly decreased from the starved to the fed value, most of the transition being achieved within the first hour of refeeding. There was a 2 h lag in the response of hepatic malonyl-CoA concentration, such that this rapid switch from oxidation to esterification could not be explained on the basis of changes in the absolute concentration of this inhibitor of carnitine palmitoyltransferase I (CPT I). Hepatic pyruvate and lactate concentrations both increased by several-fold upon refeeding and peaked after 1 h and 3 h, respectively. The hepatic lactate:pyruvate ratio increased 3.2-fold during the first 3 h of refeeding, suggesting that the cytosolic NAD(+)-NADH couple became much more highly reduced during the lag-period between the onset of inhibition of flux of fatty acids towards oxidation and the rise in malonyl-CoA concentration. This may be indicative of a lowering of intracellular pH, which would amplify greatly the sensitivity of CPT I to the inhibitor. In view of the very rapid and high food intake by these diabetic rats, the possibility is also considered that portal concentrations of amino acids and other metabolites could give rise to an increase in liver cell-volume that would inhibit CPT I acutely by an as yet unknown mechanism [M. Guzman, G. Velasco, J. Castro and V. A. Zammit (1994) FEBS Lett. 344, 239-241].

Animals↗