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At least 19 recordsLinked to original sources
PubMed2002

Production, isolation and characterization of a sterol esterase from Ophiostoma piceae.

We studied extracellular sterol esterase production by the ascomycete Ophiostoma piceae in liquid culture. Esterase activity was found in low levels in glucose medium but it was strongly induced by olive oil. An esterase was purified from the 0.5% olive oil-supplemented cultures using ultrafiltration followed by a single chromatographic step on a hydrophobic interaction column. The enzyme was a glycoprotein with 8% N-linked carbohydrate content, a molecular mass by SDS/PAGE around 56.5 kDa and an isoelectric point of 3.3. Its N-terminal sequence was TTVNVKYPEGEVV. Substrate specificity studies showed that the O. piceae esterase hydrolyzes p-nitrophenol esters, tributyrin, triolein and different cholesterol esters. Both affinity (Km) and catalytic constant (k(cat)) were positively affected by the length of the fatty acid esterifying glycerol and cholesterol. The presence of double bonds in the acyl chain increased the enzyme efficiency, although it affected the k(cat) values rather than the Km on the cholesterol esters. The O. piceae enzyme showed no interfacial activation. This enzyme could have biotechnological applications in paper manufacturing since it efficiently hydrolyzes both triglycerides and sterol esters, which form pitch deposits during manufacturing of softwood and hardwood paper pulps, respectively.

Ascomycota↗
PubMed1994

Mutations at the lysosomal acid cholesteryl ester hydrolase gene locus in Wolman disease.

The genomic sequences encoding the human lysosomal acid lipase/cholesteryl esterase (sterol esterase; EC 3.1.1.13) have been isolated and sequenced, and the information has been used to identify mutations in both alleles of the gene from a patient with Wolman disease, an autosomal recessive lysosomal lipid storage disorder. The genomic locus consists of 10 exons spread over 36 kb. The 5' flanking region is G+C-rich and has characteristics of a "housekeeping" gene promoter. One of the identified mutations involves the insertion of a T residue after position 634, resulting in the appearance of an in-frame translation stop signal 13 codons downstream. The second mutation is a T-to-C transition at nucleotide 638. This results in a leucine-to-proline substitution at amino acid 179 and is predicted to lead to the disruption of the alpha-helical structure in a highly conserved region of the protein. These mutations are each capable of completely disrupting the catalytic function of the lysosomal acid cholesteryl ester hydrolase; their presence can account for the extreme phenotype of the lysosomal lipid storage disorder manifested in members of this patient's family.

Amino Acid Sequence↗
PubMed1993

Cholesterol transport function of pancreatic cholesterol esterase: directed sterol uptake and esterification in enterocytes.

We have recently hypothesized that neutral lipids can, in part, move across biological membranes via a mechanism involving enzymes anchored to membrane proteoglycans such as those found in the brush border of the enterocyte [Bosner, M. S., Gulick, T., Riley, D. J. S., Spilburg, C. A., & Lange, L. G. (1988) Proc. Natl. Acad. Sci. U.S.A. 85, 7438-7442]. Present results now show a subsequent, essential protein-mediated sorting of neutral lipids for further intracellular metabolism. Thus, in the absence of enzyme, 0.002 pmol of cellular ester appeared after 2 h, and its level increased only 3.5-fold after 12 h. However, in the presence of cholesterol esterase, the level of cholesterol ester increased 39-fold in the same time period, indicating that the enzyme-mediated uptake accounts for 10-fold greater ester synthesis than that from basal absorption. Kinetic analysis reveals that both enzyme-mediated and background absorption depend on taurocholate concentration and are second-order reactions more likely dependent on collision than diffusion. Other lipid-recognizing proteins such as pancreatic triglyceride lipase and the intestinal fatty acid binding protein are not stimulatory to intracellular cholesterol processing. Taken together, these data suggest that pancreatic cholesterol esterase and possibly other proteoglycan-binding extracellular enzymes of neutral lipid metabolism may facilitate movement of neutral lipids into the plasma membrane and direct them into functional intracellular sites.

Animals↗
PubMed1981

Regulation of ovarian cholesterol metabolism: control of 3-hydroxy-3-methylglutaryl coenzyme A reductase and acyl coenzyme A:cholesterol acyltransferase.

Activities of enzymes involved in cholesterol metabolism were measured in ovaries of PMS-hCG-primed immature rats. Microsomal 3-hydroxy-3-methyglutaryl coenzyme A (HMG-CoA) reductase, a rate-limiting enzyme in sterol synthesis, was low during the period of maximal steroid production and cholesteryl ester storage. Acyl CoA:cholesterol acyltransferase (ACAT), the microsomal enzyme catalyzing sterol esterification and cytosolic cholesteryl ester hydrolase and mitochondrial cholesterol side chain cleavage activities, paralleled storage of sterol esters and levels of plasma progesterone, being highest on day 7 post hCG. Further experiments demonstrated that HMG-CoA reductase and ACAT are regulated by different mechanisms than the sterol esterase and cholesterol side chain cleavage system. When blood sterol levels were lowered by 4-aminopyrazolo (3,4-d)pyrimidine, plasma progestin concentrations fell and ovaries failed to accumulate sterol esters. HMG-CoA reductase increased more than 10-fold as a result of this treatment, while ACAT was 15% of that measured in controls. In contrast, cholesteryl esterase and the cholesterol side chain cleavage system were not affected. Intravenous infusion of human lipoproteins reversed the effects of 4-aminopyrazolo (3,4-d)pyrimidine. Raising blood levels up to 6-fold with either cholesterol-supplemented diets or intravenous injections of rat lipoproteins had no effect upon ovarian sterol metabolism, suggesting that the process by which blood cholesterol is utilized is saturated at normal blood sterol levels. Intravenous injection of LH on day 7 post hCG increased HMG-CoA reductase and decreased ACAT activity in addition to depleting cholesteryl esters. Prior treatment of rats with aminoglutethimide prevented the effects of LH on both HMG-CoA reductase and ACAT, indicating that changes in these enzymes were a consequence of the steroidogenic stimulus imposed by LH. Treatment with aminoglutethimide alone on day 7 post hCG did not further depress the already low HMG-CoA reductase activity, but ACAT and cholesterol ester storage were stimulated while sterol esterase activity was not altered. Aminoglutethimide also produced elevated ACAT activity and sterol ester storage in animals treated on day 2 post hCG, a time when there is normally little sterol ester accumulation. We conclude that HMG-CoA reductase and ACAT are regulated, in a reciprocal fashion, by ovarian cholesterol balance. When sufficient cholesterol is available, HMG-CoA reductase is suppressed and ACAT increases to facilitate esterification of sterol in excess of cell needs. When exogenous sterol supplies cannot meet ovarian demands, HMG-CoA reductase rises, and there is a concomitant decline in ACAT. Thus, gonadotropic control over these enzymes may be exerted, in part, through modulation of the supply of cholesterol to the ovary and/or through regulation of the rate of sterol utilization for hormone synthesis.

Acyltransferases↗
PubMed1998

Molecular cloning of the promoter for rat hepatic neutral cholesterol ester hydrolase: evidence for transcriptional regulation by sterols.

Neutral cholesterol ester hydrolase is a key enzyme in regulating hepatic free cholesterol. Using the CEH specific cDNA sequence in the 5'-untranslated region as a primer, we amplified and cloned 1.3 Kb of promoter sequence upstream of the ATG initiation codon. Analysis of the sequence revealed the presence of a consensus GC-box, which can bind the positive transcription factor Sp1, 35 bases upstream from the transcription start site. Transcriptional regulation by agents perturbing cholesterol metabolism was studied in HepG2 cells by transient transfection assays of the promoter activity in deletion constructs linked to the luciferase reporter gene. Three functional sterol response sequences were identified at positions-92, -160, and -280 of the CEH promoter. The sterol response sequence at position -92 was shown to bind SREBP-2. Therefore, the CEH gene is similar to other genes involved in regulation of cholesterol homeostasis, in that it appears to be transcriptionally regulated by sterols.

Animals↗
PubMed1993

Pathogenesis of cholesteryl lipidosis of adrenocortical and ovarian interstitial cells in F344 rats caused by tricresyl phosphate and butylated triphenyl phosphate.

Triaryl phosphates including tricresyl phosphate (TCP) and butylated triphenyl phosphate (BTP) are organophosphates used in the commercial manufacture of plastics, lubricants, and hydraulic fluids. Rat steroidogenic tissues such as adrenocortical (AC), ovarian interstitial (OI), and Leydig cells use an intracellular pathway to store cholesterol (substrate for biosynthesis of steroid hormones) as cholesteryl ester (CE). This pathway and the pathway for uptake of serum cholesterol are less used in Leydig cells of the adult male rat, resulting in a lower CE pool. BTP and TCP caused cholesteryl lipidosis in steroid hormone-synthesizing AC and OI, but not Leydig cells in the adult rat. The objectives of this study were to determine if the administration of triaryl phosphate fluids caused a defect in the cholesterol storage pathway of AC and OI cells and to determine the mechanism of action. Female rats received daily oral doses of 0 or 0.4 g/kg TCP in sesame oil vehicle or 1.7 g/kg neat BTP for 40 days. Adrenal glands from both treatment groups and ovaries from TCP-treated rats were heavier than controls. Microscopic and biochemical studies revealed cholesteryl lipidosis composed of CE in the adrenal glands and ovaries in BTP- and TCP-treated rats with the latter group affected most severely. The activity of neutral CE hydrolase (nCEH), an enzyme that converts CE to cholesterol in the uptake and storage pathways, also was inhibited most in the TCP-treated group (97% inhibition compared to that of control). The activity of acyl coenzyme A:cholesterol acyl transferase, an enzyme that esterifies cholesterol to make CE, was depressed 27% compared to that of control adrenal glands of the TCP group, resulting in elevated intracellular cholesterol levels in AC cells. An inhibition of nCEH in the storage and uptake pathways by triaryl phosphates most likely resulted in the striking accumulation of CE in cytoplasmic lipid droplets of AC and OI cells in F344 rats.

Adrenal Cortex Diseases↗
PubMed1989

Effects of cholesterol oxidation derivatives on cholesterol esterifying and cholesteryl ester hydrolytic enzyme activity of cultured rabbit aortic smooth muscle cells.

The effects of 5 micrograms/ml of 25-hydroxycholesterol; cholestane-3 beta,5 alpha,6 beta-triol; and cholesterol on acyl CoA cholesterol acyltransferase, acid cholesteryl ester hydrolase and neutral cholesteryl ester hydrolase was studied in cultured rabbit aortic smooth muscle cells. After 1 hour incubation, 25-hydroxycholesterol resulted in a fourfold stimulation of acyl CoA cholesterol acyltransferase activity. No stimulation by 25-hydroxycholesterol was noted before 15 minutes or after 5 hours of incubation. Neither cholestane-3 beta,5 alpha,6 beta-triol nor cholesterol influenced acyl CoA cholesterol acyltransferase activity at any time interval. No significant effects of any of the sterols were noted on acid cholesteryl ester hydrolase or neutral cholesteryl ester hydrolase activity. The imbalance between acyl CoA cholesterol acyl transferase and hydrolase activities induced by 25-hydroxycholesterol could result in cholesteryl ester accumulation by arterial smooth muscle cells, which may be associated with atherosclerosis.

Animals↗
PubMed1991

Effects of perturbations in hepatic free and esterified cholesterol pools on bile acid synthesis, cholesterol 7 alpha-hydroxylase, HMG-CoA reductase, acyl-CoA:cholesterol acyltransferase and cytosolic cholesteryl ester hydrolase.

Effects of expansion of the hepatic free cholesterol pool on bile acid and cholesterol metabolism and homeostasis were examined in rats fed cholesterol in high-fat diets or treated with oleyl-p-(n-decyl)-benzenesulfonate (ODS) or progesterone. Cholesterol feeding for 10-16 days, which increased free (33%) and esterified (6-fold) cholesterol, had no effect on cholate synthesis, total bile acid synthesis, or cholate turnover, whereas these activities were increased 60-80% by ODS and progesterone, which produced only small increases (19%) in free cholesterol. Cholesterol feeding reduced beta-hydroxy-beta-methylglutaryl (HMG)-CoA reductase (72%) and cholesteryl ester hydrolase (48%) and increased acyl-CoA:cholesterol acyltransferase (184%), whereas ODS and progesterone reversed these compensatory responses in cholesterol-fed rats. Cholesterol 7 alpha-hydroxylase was changed no more than 22% by any treatment. A bolus of ODS elevated biliary cholesterol output 41% and shifted biliary bile acid synthesis and composition toward 12-deoxy bile acids. These effects were not seen in ODS-fed or progesterone-treated rats, in which cholesteryl ester stores were depleted. It is concluded that effects of free cholesterol on bile acid synthesis and biliary cholesterol are probably mediated by specific precursor or regulatory pools which can be independently regulated and which represent a relatively small fraction of hepatic free cholesterol.

Animals↗
PubMed1993

The esterification of cholesterol in the yolk sac membrane of the chick embryo.

The uptake of lipid from the yolk by the yolk sac membrane of the chick embryo is accompanied by the rapid esterification of a large proportion of the yolk cholesterol. This could arise from enhanced acyl-CoA:cholesterol acyltransferase (ACAT) activity and/or inhibition of cholesteryl ester hydrolase (CEH) activity. The activity of ACAT was therefore measured in microsomes obtained from yolk sac membranes at various stages of development. A high level of activity (up to 929 pmol of cholesteryl oleate formed per min per mg protein) was found during the second half of this period. Supplementation with exogenous cholesterol stimulated ACAT activity in microsomes obtained from the tissue at the earlier, but not at the later, stages of development suggesting that the enzyme became saturated with microsomal cholesterol as development proceeded. Correlating with this, the concentration of cholesterol in the microsomes increased 4-fold between 9 and 20 d of development. The activity of CEH was very low in the microsomes and could not be detected in the cytosolic fraction. The activity of a protein, which has been shown to function as an inhibitor of CEH, was found to be present at all stages of development. The high activity of ACAT, together with the low activity of CEH and an active CEH inhibitor protein is a combination well suited to promote an essentially unidirectional conversion of cholesterol to cholesteryl ester. This process may be a major determinant of the rate of lipid transfer from the yolk to the embryo.

Animals↗
PubMed1994

The effects of clofibrate and bezafibrate on cholesterol metabolism in the liver of the male rat.

Fibric acid derivatives are used to treat hyperlipidemia and have wide ranging effects on lipid metabolism. The action of these compounds on cholesterol esterification, catalyzed by acyl-coenzyme A:cholesterol acyltransferase (ACAT), has been quite widely studied, but their effect on cholesteryl ester hydrolysis and the enzyme neutral cholesteryl ester hydrolase (nCEH) has been largely ignored. Male rats were therefore fed for 10 d on a standard chow diet supplemented with either clofibrate or bezafibrate, to study their effects on plasma lipid levels and hepatic cholesterol metabolism. Plasma triacylglycerols were not significantly altered by these diets, but bezafibrate significantly lowered plasma cholesterol levels (29.7%, P < 0.01). When expressed per unit weight of DNA, both fibrates reduced the hepatic content of triacylglycerol, cholesterol and cholesteryl esters (40, 18.7, 16.5 and 66.7, 28.6, 34.2% for clofibrate and bezafibrate, respectively). ACAT activity was significantly reduced by both drugs, but clofibrate (65% inhibition) was more effective than bezafibrate (35% inhibition). The most dramatic effect of the diets was a marked increase in the activity of both the microsomal and the cytosolic nCEH. When expressed on a whole liver basis, the effect of bezafibrate on the cytosolic enzyme (13.6-fold increase in activity) was much greater than that of clofibrate (4.8-fold increase). Increases in the activity of a cytosolic protein that inhibits the activity of nCEH were also noted, but these changes were relatively small. The results suggest that the activation of nCEH, in combination with the inhibition in ACAT activity, contributes to a decrease in the cholesteryl ester content of the liver which may influence the secretion of very low density lipoprotein.

Animals↗
PubMed1995

The effects of simvastatin and cholestyramine, alone and in combination, on hepatic cholesterol metabolism in the male rat. off.

The influence of dietary simvastatin, cholestyramine, and the combination of simvastatin plus cholestyramine on hepatic cholesterol metabolism has been investigated in male rats. Recovery from the effects of the drugs was also investigated by refeeding normal chow for 24 h. Both drugs, alone and in combination, increased 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase activity in vitro, but activity returned toward control values, after drug withdrawal. Acyl-CoA:cholesterol acyltransferase (ACAT) was significantly reduced (P < 0.001) by simvastain (-75%), cholestyramine (-71%), and by the drug combination (-81%), due both to a decrease in microsomal cholesterol and to nonsubstrate-dependent modulation of enzyme activity. Refeeding control diet increased ACAT activity but not to control levels. The enhanced activity arose partly from higher microsomal cholesterol and partly from increases in total enzyme activity. Cytosolic neutral cholesteryl ester hydrolase (CEH) activity was substantially elevated by simvastatin (3-fold) and by the drug combination (6-fold), whereas the effect of cholestyramine was smaller (1.5-fold). Normal chow for 24 h only partially returned cytosolic CEH activity to control values. Microsomal CEH activity was increased by simvastatin, alone and in combination with cholestyramine (1.4 to 1.7-fold), and was also enhanced, in the cholestyramine-treated animals, following drug withdrawal. Removal of simvastatin did not allow recovery of this enzyme activity, while withdrawal of the drug combination led to values 29% below controls. The results indicate that in the rat, simvastatin and cholestyramine alter both ACAT and CEH activity, as well as inhibiting HMG-CoA reductase activity.

Animals↗
PubMed1997

Effect of trifluoperazine on certain arterial wall lipid-metabolizing enzymes inducing atherosclerosis in rhesus monkeys.

The effect of trifluoperazine (TFP) was investigated on arterial wall lipid-metabolizing enzymes like acyl-CoA:cholesterol acyltransferase (ACAT) and cholesterol ester hydrolase (CEH) in rhesus monkeys. The activity was determined in aortic wall homogenates obtained from rhesus monkeys fed an atherogenic diet coupled with intramuscular injections of adrenaline and TFP. Although TFP had no significant effect on serum cholesterol and triglycerides, it decreased significantly the formation of atherosclerotic lesions by decreasing the esterification of cholesterol, by inhibiting ACAT and enhancing its utilization by activating CEH. Hence, the preventive effect of TFP on the development of atherosclerosis in rhesus monkeys is mediated through its ability to influence the activities of arterial wall lipid-metabolizing enzymes like ACAT and CEH.

Animals↗
PubMed1997

In vitro effect of garlic powder extract on lipid content in normal and atherosclerotic human aortic cells.

In the present study, the mechanism of the in vitro effect of garlic powder extract (GPE) on lipid content of cultured human aortic cells was investigated. The addition of GPE abolished atherogenic blood serum-induced accumulation of free cholesterol, triglycerides, and cholesteryl esters in smooth muscle cells derived from uninvolved (normal) intima. In cells isolated from atherosclerotic plaque, GPE lowered these lipids. GPE inhibited lipid synthesis both in normal and atherosclerotic cells. It inhibited acyl-CoA:cholesterol acyltransferase activity that participates in the cholesteryl ester formation and stimulated cholesteryl ester hydrolase that degrades cholesteryl esters. This may explain the lipid reduction caused by GPE in atherosclerotic cells. GPE inhibited the uptake of modified low density lipoprotein and degradation of lipoprotein-derived cholesteryl esters, thus considerably reducing the intracellular accumulation of cholesteryl esters. This suggests the mechanism responsible for the prevention of lipid accumulation in aortic cells caused by atherogenic blood serum.

Adult↗
PubMed1999

Hepatic zonation of the formation and hydrolysis of cholesteryl esters in periportal and perivenous parenchymal cells.

The periportal (PP) and perivenous (PV) zones of the liver acinus differ in enzyme complements and capacities for cholesterol and bile acid synthesis and other metabolic processes. The aim of this investigation was to determine the acinar distribution of the catalytic activity of the enzymes governing the formation and hydrolysis of cholesteryl esters using PP and PV hepatocytes from normal or cholestyramine-fed rats. The hepatocyte subpopulations were isolated by centrifugal elutriation, characterized according to the distribution pattern of a number of cell parameters and marker enzymes, and assayed for acyl-CoA:cholesterol acyltransferase (ACAT) and lysosomal, cytosolic and microsomal cholesteryl ester hydrolase (CEH). In normally fed rats, no zonation was found in the activity of lysosomal CEH and ACAT, and the activity of both cytosolic and microsomal CEH zonated toward the PV zone of the acinus. Concentrations of free and esterified cholesterol in homogenates, cytosol, and microsomes of PP and PV cells were, however, similar. Cholestyramine raised significantly the PV/PP ratio of ACAT because of an exclusive PP reduction of activity and abolished the heterogeneity in microsomal CEH because of a greater inhibitory PV response, whereas the PV dominance of cytosolic CEH and the homogeneous distribution of lysosomal CEH were unaffected. These results demonstrated homogeneity within the liver acinus for the enzymatic degradation of endocyted lipoprotein-derived cholesteryl esters, a structural zonation of the cytosolic CEH and a dynamic zonation of ACAT and the microsomal CEH, with a PV dominance of the enzymatic capacity for the degradation of stored cholesteryl esters in normal livers.

Animals↗
PubMed1977

Uptake and degradation of cholesterol ester-labelled rat plasma lipoproteins in purified rat hepatocytes and nonparenchymal liver cells.

1. A new method for isolation and purification of rat liver hepatocytes and nonparenchymal cells by differential centrifugation is described. 2. Cholesterol ester-labelled lipoproteins (prepared by the action of lecithin: cholesterol acyltransferase) intravenously injected were taken up by hepatocytes and nonparenchymal cells. 3. Hepatocytes and nonparenchymal cells in suspension were able to take up and hydrolyse the cholesterol ester portion of lipoproteins. 4. Uptake of cholesterol ester labelled whole rat plasma and high density lipoproteins (HDL) increased with increasing concentrations until a distinct saturation level was reached in hepatocytes. In nonparenchymal cells there was no saturation of lipoprotein uptake. 5. Concanavalin A inhibited cholesterol ester-labelled lipoprotein uptake in hepatocytes, indicating that the uptake at least partially depends on carbohydrate sites on the cell surface. The uptake in nonparenchymal cells was unaffected of concanavalin A. 6. The specific activity of the acid cholesterol ester hydrolase was the same in homogenates from hepatocytes and nonparenchymal cells while acyl-CoA: cholesterol acyltransferase was found almost exclusively in hepatocytes.

Acid Phosphatase↗
PubMed1977

The effect of bile salts on the formation and hydrolysis of cholesterol esters by rat liver enzymes.

To determine the effects of different bile salts on the enzymic esterification of cholesterol and the hydrolysis of cholesterol esters rat liver homogenates and rat liver microsomes were incubated with varying amounts of different bile salts. Bile salts inhibited the formation of radioactive cholesterol esters in incubations of either rat liver homogenates or rat liver microsomes containing [14C]cholesterol. Chenodeoxycholate, glycochenodeoxycholate and taurochenodeoxycholate were more potent inhibitors than their comparable cholate analogues. Bile salts stimulated the hydrolysis of cholesterol esters when incubation were carried out with the liver homogenates. The dihydroxy bile salts were again more potent in this regard than the trihydroxylated bile salts. When the effects of bile salts on cholesterol ester hydrolysis were studied in in vitro incubations of hepatic microsomes a biphasic mode of acion was observed. In the absence of Na+ or K+ bile salts stimulated the hydrolysis of cholesterol oleate. However, following the addition of either Na+ or K+ to the microsomal incubations, bile salts caused an inhibition of cholesterol ester hydrolysis. Since cholesterol esterification was also inhibited under these conditions a direct inhibitory effect (not attributable to enhanced hydrolase activity) of the bile salts on the formation of cholesterol esters by the microsomes was established. Furthermore, this inhibition takes place at the transacylation step involving the fatty acyl-CoA ester and the sterol. These results suggest that bile salts can significantly alter the cholesterol-cholesterol ester profile in the liver, and furthermore, that these effects may be influenced by small changes in the intracellular environment in the region where these reactions occur.

Acyltransferases↗
PubMed1981

Studies on the activity of acyl-CoA:cholesterol O-acyltransferase and acid cholesterol ester synthetase in rat aortas.

Acyl-CoA: cholesterol O-acyltransferase (ACAT) activity was measured in microsomal preparations from rat aorta (intima-media) with [14C]oleoyl CoA and endogenous cholesterol as substrates. The specific activity of ACAT in liver and adrenal microsomal preparations was 10--20-times greater than ACAT activity in aortic microsomes; no ACAT activity could be detected in fat pad microsomes. ACAT activity in liver and adrenal microsomes was enhanced by the addition of exogenous cholesterol. In contrast, exogenous cholesterol did not increase ACAT activity in rat aortic microsomes. Levels of endogenous cholesterol and ACAT activity in microsomal preparations from rat aorta were not reduced when circulating plasma cholesterol levels were decreased by the administration of 4-aminopyrazolopyrimidine to rats. Acid cholesterol ester synthetase activity was not detectable in high-speed supernatant fractions from rat aorta; low levels of activity could be measured in rat aorta microsomal preparations but this was less than 10% of ACAT activity. Thus, ACAT would seem to be the principal enzymatic route for the synthesis of cholesterol esters in aorta.

Acyltransferases↗