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PubMed1989

[Enzymatic methyl esterification of the protein in bovine crystalline lens in culture].

In the present paper a study on the enzymatic methyl esterification of proteins in the bovine lens has been presented. The data obtained show that the synthesis of the methyl donor (AdoMet) as well as the methyl esterification of proteins are operative in the lens incubated in the presence of L-(methyl-14C) methionine and the amount of labelled methyl esters decreases during cell ageing. Furthermore, the Authors suggest the usefulness of this model system in the evaluation of the overall AdoMet metabolism in aging.

Animals↗

PubMed1989

Effects of Bay o 2752, a hypocholesterolemic agent, on intestinal taurocholate absorption and cholesterol esterification.

Bay o 2752 [N,N'-(1, 11-undecandiyl)bis(2,3-dihydro-2-methyl-1H-indole-1-carboxamide)] has been demonstrated in rats to inhibit intestinal cholesterol absorption. Studies were carried out in male Wistar rats to determine if the mechanism is inhibition of intestinal bile acid absorption or cholesterol esterification. Bay o 2752 did not alter intestinal bile acid absorption as measured by in vitro uptake of [14C]taurocholic acid into ileal everted sacs (0.01 and 1.0 mg/ml of Bay o 2752) or the biliary excretion of radioactivity after in vivo ileal perfusion of the bile acid and drug (1.0 mg/ml at 1.0 ml/min for 1 hr). Cholesterol esterification was determined by measurement of in vitro activity of acyl coenzyme A:cholesterol acyltransferase from hepatic microsomes and cholesterol ester hydrolase from pancreatic supernatant, and the in vivo lymphatic output of cholesteryl ester after intraduodenal cholesteryl infusion. Addition of Bay o 2752 (0.01-10 micrograms/ml) to hepatic microsomes produced a concentration-dependent decrease in acyl coenzyme A:cholesterol acyltransferase activity with an IC50 of 0.95 micrograms/ml. Cholesterol ester hydrolase activity was unaffected by the drug (1.0-100 micrograms/ml). Intraduodenal infusion of Bay o 2752 (10 mg/ml at 0.9 ml/hr for 8 hr) reduced markedly the flux of cholesterol from the intestinal lumen into the mesenteric lymph, especially the lymphatic output of the esterified form of both radioisotopically labeled and total cholesterol. These data suggest that Bay o 2752-induced reduction in intestinal cholesterol absorption results from its potent inhibitory effect on acyl coenzyme A:cholesterol acyltransferase activity.

Animals↗

PubMed1987

Esterification of cholesterol in high density lipoprotein decreases its ability to support ACTH-stimulated steroidogenesis by rat adrenocortical cells.

Addition of high density lipoprotein 3 (HDL3) isolated from human plasma of d greater than 1.125 g/ml which had been preincubated for 24 h at 37 degrees C enhanced steroidogenesis by cultured rat adrenal cells only 38% as well as HDL3 isolated from unincubated plasma. Loss of steroidogenic activity due to preincubation was associated with a decrease in the percent HDL3 cholesterol remaining unesterified. Inhibition of lecithin-cholesterol acyltransferase activity by heating (60 degrees C, 1 h) or addition of dithionitrobenzoic acid (1.4 mM) prevented esterification of cholesterol in HDL and also prevented loss of steroidogenic activity. Although incubation of plasma of d greater than 1.125 g/ml prior to isolation caused cholesterol esterification, there was no change in the ratio of total cholesterol to protein in HDL, size and shape of the HDL particle as assayed by measurement of sedimentation velocity, nor affinity for the putative HDL receptor. Addition of unesterified cholesterol to preincubated HDL restored steroidogenic activity. These results indicate that unesterified cholesterol in HDL is preferentially used as substrate for rat adrenal steroidogenesis. The effects of nonlipoprotein serum proteins on HDL action in the adrenal were also examined. The ability of HDL3 to enhance rat adrenal steroidogenesis was not significantly less in serum-free media than in media supplemented with lipoprotein-poor fetal calf serum or human plasma of d greater than 1.21 g/ml, suggesting that rat adrenal uptake of HDL cholesterol does not depend on participation of plasma enzymes or transport proteins.

Adrenal Cortex↗

PubMed1986

The plasma cholesterol concentration and cholesterol esterification rate in patients with stage I-III arterial hypertension.

Disorders of cholesterol metabolism were studied in 88 patients with essential or renovascular hypertension, among whom the individual stages of the disease, classified by WHO criteria, were evenly represented. The results were compared with the findings in a group of 87 healthy controls. The following were determined in the plasma: the total (TCH) and free (FCH) cholesterol concentration, triglycerides (TG) and lecithin cholesterol acyltransferase (LCAT) activity, defined as the molar esterification rate (MER). The MER/FCH ratio gave the fractional esterification rate (FER) as the percentage per hour. In evaluation of the whole group of hypertensive patients, the mean TCH values were found to be raised (6.62 as against 6.05 mmol/l, P less than 0.05), but FCH levels were raised more significantly (mean 1.76 as against 1.51 mmol/l, p less than 0.001). With normal MER values, the hypertensive group had a significantly lower mean FER value (5.45 as against 6.27 %/h, p less than 0.001). Mainly patients with stage II and III hypertension accounted for the reduced rate of cholesterol recirculation between plasma and tissues (i.e. the FER value). The findings indicate that a change from stage I to stage II hypertension is accompanied by an increased incidence of lipid metabolism disorders.

Cholesterol↗

PubMed1988

CoA- and non-CoA-dependent retinol esterification in retinal pigment epithelium.

Washed, buffered microsomes from bovine retinal pigment epithelium catalyze retinyl ester synthesis from retinol in the absence of an exogenous acyl donor. A plot of retinyl ester synthesis versus time reaches a plateau at 123 +/- 26 nmol of retinyl ester mg-1 microsomal protein, providing a minimum value of the concentration of the endogenous acyl donor. Fatty acyl-CoA analysis by three different methods employing high performance liquid chromatography resulted in the detection of less than 1 nmol mg-1 protein of acyl-CoA, indicating that fatty acyl-CoA is not the endogenous acyl donor. Stimulation of the rate of retinyl ester synthesis by palmitoyl-CoA or ATP, CoA, and palmitate is observed following its addition at the beginning of the reaction or after the endogenous acyl source has been exhausted by 20 min of reaction with retinol. Palmitate from [14C]palmitoyl-CoA is incorporated into retinyl ester at a rate similar to that for the incorporation of [3H] retinol, demonstrating the presence of an apparent acyl-CoA:retinol acyl transferase activity. The acyl group from palmitoyl-CoA can be transferred initially to a component of the microsomes and subsequently to retinol. The product of retinyl ester synthesis from all-trans-retinol and palmitoyl-CoA is all-trans-retinyl palmitate, indicating that the stereochemical configuration is retained during esterification. The kinetic parameters for the esterification of 11-cis-retinol and all-trans-retinol are similar.

Acyl Coenzyme A↗

PubMed1987

Regulation of cholesterol esterification by micellar cholesterol in CaCo-2 cells.

The regulation of acylcoenzyme A:cholesterol acyltransferase (ACAT) activity by cholesterol was studied in an established enterocyte cell line. CaCo-2 cells were grown in culture to confluency and dome formation. They were characterized morphologically by light and transmission electron microscopy. During the culture period, ACAT activity remained stable while the activities of the brush border enzymes sucrase and alkaline phosphatase progressively increased with time and plateaued 12 days after plating. As determined by the rate of incorporation of oleic acid into the individual lipid classes, the rate of triglyceride synthesis was twice that of phospholipid and 15 times that of cholesteryl ester synthesis in these cells. Incubating CaCo-2 cells with cholesterol solubilized in taurocholate micelles resulted in a significant increase in ACAT activity (149 +/- 5 pmol/dish per 2 hr vs. 366 +/- 5, (P less than 0.001) without changing the rates of triglyceride or phospholipid synthesis. The stimulation of ACAT activity by micellar cholesterol was rapid, occurring within 5 min and reaching a maximal effect by 2 hr. The regulation of ACAT activity by cholesterol was directly dependent upon the concentration of cholesterol solubilized in the micelle and was independent of protein synthesis. Incubating CaCo-2 cells with micellar cholesterol did not increase the esterification of, nor did the cholesterol enter the pool of, newly synthesized or performed cholesterol within 2 hr. The micellar cholesterol that was taken up by the cells was esterified within 5 min after starting the incubation. Progesterone, a known ACAT inhibitor, significantly decreased the rate of esterification of intracellular micellar cholesterol proving that the cholesterol taken up by CaCo-2 cells was indeed entering the ACAT pool. Despite increasing amounts of unesterified cholesterol entering the cells via micelles, the percent of cholesterol that was esterified at any one time remained constant at 1%. The results suggest that ACAT activity in CaCo-2 cells is stimulated by cholesterol delivered to the cells by way of taurocholate micelles. The rapid entry of this sterol into the ACAT substrate pool suggests that ACAT activity in CaCo-2 cells is regulated by the expansion of the cholesterol substrate pool that is being utilized by an unsaturated ACAT enzyme.

Cells, Cultured↗

PubMed1986

Type C Niemann-Pick disease. A parallel loss of regulatory responses in both the uptake and esterification of low density lipoprotein-derived cholesterol in cultured fibroblasts.

Low density lipoprotein (LDL) internalization by mutant type C Niemann-Pick (NPC) fibroblasts results in uptake of excess total cholesterol. Uptake of excess lipoprotein cholesterol appears to be mediated by the specific LDL receptor pathway. Associated with excessive LDL-cholesterol uptake is a lesion in early intracellular cholesteryl ester synthesis. In vitro acylCoA:cholesterol acyltransferase activity is normal in cell-free extracts of mutant cells. The ability of exogenous sterols to enhance intracellular esterification of [3H]mevalonate-derived [3H]cholesterol was severely limited in mutant cell cultures suggesting that in vivo activation and/or expression of activated acylCoA:cholesterol acyltransferase may be compromised by the primary mutation of type C Niemann-Pick disease. After 2 days of LDL uptake, rates of intracellular cholesteryl ester synthesis in mutant cells paralleled the rates of esterification in normal cells suggesting that specific early in vivo expression of the acyltransferase may be affected in this disorder.

Biological Transport↗

PubMed1987

Acyl-CoA-independent esterification of retinol bound to cellular retinol-binding protein (type II) by microsomes from rat small intestine.

Cellular retinol-binding protein (type II) (CRBP(II)), a newly described retinol-binding protein, is present in the small intestinal absorptive cell at high levels. Retinol (vitamin A alcohol) presented as a complex with CRBP(II) was found here to be esterified by microsomal preparations from rat small intestinal mucosa. The esterification observed utilized an endogenous acyl donor(s) and produced retinyl esters containing linoleate, oleate, palmitate, and stearate in a proportion quite similar to that previously reported for retinyl esters in lymph and isolated chylomicrons of rat. No dependence on endogenous or exogenous acyl-CoA could be demonstrated. The apparent Km for retinol-CRBP(II) in the reaction with endogenous acyl donor was 2.4 X 10(-7) M. Retinol presented as a complex with CRBP(II) was esterified more than retinol presented as a complex with cellular retinol-binding protein or retinol-binding protein, two other proteins known to bind retinol in vivo, but about the same as retinol presented bound to bovine serum albumin or beta-lactoglobulin. The ability of protein-bound retinol to be esterified was related to accessibility of the hydroxyl group, as judged by the ability of alcohol dehydrogenase to oxidize the bound retinol. However, whereas retinol bound to CRBP(II) was unavailable for esterification in any acyl-CoA-dependent reaction, retinol bound to bovine serum albumin was rapidly esterified in a reaction utilizing exogenous acyl-CoA. The results suggest that one of the functions of CRBP(II) is to accept retinol after it is absorbed or generated from carotenes in the small intestine and present it to the appropriate esterifying enzyme.

Acyl Coenzyme A↗

PubMed1985

Lipoprotein abnormalities in primary biliary cirrhosis. Association with hepatic lipase inhibition as well as altered cholesterol esterification.

The nature and etiology of plasma lipoprotein abnormalities in patients with varying stages of primary biliary cirrhosis (PBC) were assessed. Two distinct lipoprotein patterns were observed. In patients with early and intermediate histologic stages of PBC, mild elevations of very low density lipoproteins and low density lipoproteins (LDLs), and marked increases in high density lipoproteins (HDLs) were often noted (group 1). In contrast, patients with advanced disease had marked elevations in LDLs with the presence of lipoprotein-X, and a significant decrease in HDLs (group 2). The lipoprotein pattern in group 1 was characterized by a normal ratio of free cholesterol to total cholesterol, whereas in group 2, this ratio was elevated. In plasma from group 1 patients only spherical micelles were observed on electron microscopy, whereas in plasma from group 2 patients bilayered disks could be seen in LDLs and HDLs. The increase in HDLs observed in group 1 subjects was associated with elevations in HDL2, whereas in group 2 subjects only very low amounts of HDL3 were observed on analytic ultracentrifugation. Mean plasma apolipoprotein B and C-II concentrations were increased in both groups; but apolipoprotein A-I and AII values were divergent, with group 1 subjects having elevated values,and group 2 subjects having decreases values. Mean postheparin hepatic lipase activity was decreased in both groups of patients with PBC due to the presence of an inhibitor in PBC plasma, while altered cholesterol esterification was only observed in group 2. These data indicate that hepatic lipase inhibition may play an important role in the pathogenesis of the lipoprotein abnormalities seen in early and intermediate PBC, and these abnormalities are then further modified by altered cholesterol esterification in advanced disease.

Adult↗

PubMed1973

Esterification of fatty acids at room temperature by chloroform-methanolic HCl-cupric acetate.

A new procedure for the preparation of methyl esters from free fatty acids under mild conditions was investigated. Free fatty acids are dissolved in a mixture of chloroform-methanolic HCl-cupric acetate and kept at room temperature for 30 min for complete esterification. The method is suitable for esterification of long-chain acids, such as 18:0, and for very long chain acids, such as 24:0. Fatty acids from brain glycerophosphatides, which included a high concentration of polyenes such as 20:4 (n - 6), 22:4 (n - 6), and 22:6 (n - 3), were also esterified by the same procedure, and neither artifact formation nor loss of unsaturated acids was observed.

Carbon Isotopes↗

PubMed1984

A genetic storage disorder in BALB/C mice with a metabolic block in esterification of exogenous cholesterol.

Cholesterol metabolism has been investigated in a strain of BALB/C mice that carry an autosomal recessive mutation associated with decreased sphingomyelinase and glucocerebrosidase activity and storage of sphingomyelin and glucocerebroside as well as cholesterol in lysosomes (Pentchev, P. G., Gal, A. E., Boothe, A. D., Omodeo-Sale, F., Fouks, J., Neumeyer, B. A., Quirk, J. M., Dawson, G., and Brady, R. O. (1980) Biochim. Biophys. Acta 619, 669-679). When affected animals are placed on a diet high in cholesterol, they develop hepatomegaly associated with an extensive accumulation of unesterified cholesterol in the liver. Cultured skin fibroblasts derived from these mice also manifest a defect in cholesterol esterification although the uptake and intracellular location of exogenous cholesterol is comparable to that of controls. Microsomal fatty acyl-CoA:cholesterol acyltransferase activity was normal or elevated in extracts of tissues from the affected animals. Furthermore, the subcellular distribution and membrane orientation of acyl-CoA:cholesterol acyltransferase appeared normal in microsomal preparations isolated from affected mice. The blockage of esterification of exogenous cholesterol in the presence of normal transferase activity is suggestive of a defect in a component involved in the intracellular disposition of this sterol. The attenuation in tissue levels of sphingomyelinase and glucocerebrosidase and the accumulation of sphingolipids may reflect alterations in lysosomal function resulting from an imbalance of unesterified cholesterol in these organelles.

Acyltransferases↗

PubMed1984

Sites of methyl esterification and deamination on the aspartate receptor involved in chemotaxis.

The receptors involved in bacterial chemotaxis are post-translationally modified by specific enzymes which catalyze the deamination of glutaminyl residues and the methyl esterification and demethylation of glutamyl residues. In this work we identify the sites of these covalent modifications on the aspartate receptor from Salmonella typhimurium. These were identified using the properties of the Staphylococcus aureus V8 protease which cleaves peptide bonds following glutamyl but not glutaminyl residues. We show here that bonds following methyl-esterified glutamyl residues are also resistant to the protease. A comparison of the fragments obtained after V8 protease cleavage of methyl-esterified (or deaminated) peptides with the fragments from the corresponding unmodified peptides immediately yields the sites of modification. Three of the four methyl-esterified glutamyl residues are located near the middle of the receptor amino acid sequence; one of these is synthesized as a glutaminyl residue and is deaminated by the esterase to form a glutamyl residue. The fourth site of methyl esterification is located near the carboxyl terminus. All four sites occupy analogous positions in a well-conserved arrangement of residues which may form a binding site for the esterase and the methyltransferase.

Amino Acid Sequence↗

PubMed1983

Concerted stimulation and inhibition of desaturation, chain elongation, and esterification of essential fatty acids by cultured neuroblastoma cells.

Neuroblastoma (N1E-115) cells in culture rapidly incorporated exogenous fatty acyl chains suspended as albumin complexes in the medium. The essential fatty acids, linoleic (18:2(n - 6)) and linolenic (18:3(n - 3)) acids, were converted to polyunsaturated acids by delta 6 and delta 5 desaturation and chain elongation. The major end products (20:4 from 18:2(n - 6) and 20:5 and 22:5 from 18:3(n - 3)) were preferentially esterified to phospholipids, whereas intermediates were esterified primarily or equally to triacylglycerol. The effects of unlabeled exogenous fatty acids (eg. 40 microM 18:2(n - 6), 18:3(n - 6), 18:3(n - 3), 20:3(n - 6), 20:4(n - 6), trans-18:2(n - 6), 18:1(n - 9), trans-18:1(n - 9), or 16:0) on the conversion of 2 microM [1-(14)C]18:2(n - 6), 18:3(n - 3), 20:3(n - 6), 20:4(n - 6), or 16:0 and on accumulation of products and unaltered substrates in phospholipids and triacylglycerol were examined after incubations of 2-24 h. With [1-(14)C]18:2, formation and esterification of 20:4 to phospholipids was (i) stimulated 4-8-fold by 18:2(n - 6), 20:3(n - 6), or 20:4(n - 6), (ii) inhibited by 18:3(n - 3) or trans-18:2(n - 6), or (iii) unaffected by 18:3(n - 6), 18:1(n - 9), trans-18:1(n - 9), and 16:0. Specific but less marked effects were observed with the other 1-(14)C-substrate acids. Thus, various fatty acids influenced the metabolism of essential fatty acids both at the level of conversion by desaturation and elongation and at esterification to complex lipids by mechanisms specific to individual acids. Product inhibition was not a major feedback mechanism; however, the complement of available fatty acids evidently modulates the acyl chain composition of membrane phospholipids through processes in addition to acyltransferase selectivity. The data support a closely coordinated or concerted enzyme system for directed synthesis of esterified polyunsaturated acyl chains.

Animals↗

PubMed1981

A comparative study on the rate of de-esterification of dexamethasone phosphate and dexamethasone sulfate in synovial fluids.

Considering the importance of the 21-OH group in promoting the anti-inflammatory activity of the steroids, it is possible that differences in the rate of hydrolysis of steroid esters may influence the potency of pharmacological activity of the steroids (Polley and Mason, 1950, Goldfien, et al., 1955). In the present paper the rate of de-esterification of the steroid esters in human synovial fluids was studied in vitro. Hydrolytic rates of dexamethasone-21-sulfate (DS) and dexamethasone-21-phosphate (DP) in synovial fluids aspirated from the knee joint of 10 patients each with rheumatoid arthritis and osteoarthritis of the knee measured by radioimmunoassay. DP was hydrolyzed to the extent of 10%, 30%, 50%, 80% after incubation for 1, 3, 6, 24 hours respectively. On the other hand, DS was hydrolyzed to the extent of less than 10% even after incubation for 24 hours. The difference between the rate of de-esterification of DP and DS for each period was statistically highly significant (p less than 0.001). These results suggest that DP is hydrolyzed in synovial fluids much faster than DS and converted into free dexamethasone which may exhibit a powerful anti-inflammatory action.

Arthritis, Rheumatoid↗

PubMed1982

[Cholesterol esterification in human plasma].

The initial rates of the reaction catalized by the lecithin: cholesterol acyltransferase, were measured in the plasmas of two groups of normal subjects (20 males and 20 females) of the same age (average 20 years). The determination of the initial rate of lecithin: cholesterol acyltransferase reaction in human plasma was measured by a method based on the determination of plasma unesterified cholesterol by gas-liquid chromatography. With this technique the plasma esterification reaction is linear to approx. 75 min. The influence of sex, concentration of cholesterol total, high density lipoprotein cholesterol and unesterified cholesterol on the initial rate of plasma cholesterol esterification has been shown.

Adult↗

PubMed1980

Cholesterol esterification of mechanically-induced aortic lesions in normolipemic pigs.

Intimal thickenings were produced in the abdominal aortae of normolipemic pigs by longitudinal mechanical injury. In two-week lesions there was increased I-14C-oleic acid incorporation into esterified cholesterol (CE), accompanied by lipid droplet formation. In twelve-week lesions, lipid droplets had largely disappeared, and the incorporation of 1-14C-oleic acid into CE was similar to that of normal aorta. Increased esterification of cholesterol with oleic acid may be a protective mechanism during the early phases of the arterial repair reaction. Regression of the lesions may be associated with the return of cholesterol esterification activity to normal.

Animals↗

PubMed1998

Adsorptive control of water in esterification with immobilized enzymes: I. Batch reactor behavior.

Reducing the influence of an undesired product in an enzymatic reaction could have a significant impact on the productivity of such systems. Here, we focus on the removal of water formed during an enzymatic esterification in a batch reactor. A commercial immobilized lipase preparation, known as Lipozyme, is used as the biocatalyst and propionic acid and isoamyl alcohol dissolved in hexane are the substrates. In this system, the water formed will partition between the catalyst and the medium. As the more polar reactants are converted into the less polar ester product, the water is partitioned more towards the biocatalyst and the accumulation of water eventually causes lower reaction rates. Addition of a strong-acid cation exchange resin in sodium form is found to control the water accumulation on the biocatalyst without stripping the essential water needed for the enzyme to function and substantial improvements in conversion are achieved. A mathematical model is developed to describe the batch reaction behavior with and without added absorbent, which successfully predicts the behavior of water and its effects.

Adsorption↗

PubMed1998

Adsorptive control of water in esterification with immobilized enzymes: II. fixed-bed reactor behavior.

Experimental and theoretical studies are conducted to understand the dynamic behavior of a continuous-flow fixed-bed reactor in which an esterification is catalyzed by an immobilized enzyme in an organic solvent medium. The experimental system consists of a commercial immobilized lipase preparation known as Lipozyme as the biocatalyst, with propionic acid and isoamyl alcohol (dissolved in hexane) as the reaction substrates. A complex dynamic behavior is observed experimentally as a result of the simultaneous occurrence of reaction and adsorption phenomena. Both propionic acid and water are adsorbed by the biocatalyst resulting in lower reaction rates. In addition, an excessive accumulation of water in the reactor leads to a rapid irreversible inactivation of the enzyme. A model based on previously-obtained adsorption isotherms and kinetic expressions, as well as on adsorption rate measurements obtained in this work, is used to predict the concentration and thermodynamic activity of water along the reactor length. The model successfully predicts the dynamic behavior of the reactor and shows that a maximum thermodynamic activity of water occurs at a point at some distance from the reactor entrance. A cation exchange resin in sodium form, packed in the reactor as a selective water adsorbent together with the catalyst particles, is shown to be an effective means for preventing an excessive accumulation of water formed in the reaction. Its use results in longer cycle times and greater productivity. As predicted by the model, the experimental results show that the water adsorbed on the catalyst and on the ion exchange resin can be removed with isoamyl alcohol with no apparent loss in enzyme activity.

Adsorption↗