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1.
Cupric ions were administered subcutaneously to male Sprague-Dawley rats at a single dose of 200 μmol/kg. At 24 hr after administration,
a remarkable increase of total and free cholesterol was seen in the rat serum. Also, when lecithin-cholesterol acyltransferase
(LCAT) (E.C. 2.3.1.43) activity was expressed as the percentage of the total serum that free cholesterol esterified, the acyltransferase
activity in rats treated with cupric ions showed a slight decrease while the triglyceride content in rat serum and liver decreased
by 54% and 61%, respectively. However, the content of hepatic cholesterol in rats treated with cupric ions did not show such
a marked change.
On the other hand, acid cholesteryl ester hydrolase activity (Acid CEH) (E.C. 3.1.1.14) in liver lysosomes of rats treated
with cupric ions showed a marked decrease with increasing cupric ion concentration both in vivo and in vitro. Furthermore,
cupric ions caused a marked release of the lysosomal enzymes cathepsin D and β-glucuronidase into the cytosolic fraction.
The changes in acid cholesteryl ester hydrolase activity induced by cupric ions appear to be a direct effect of cupric ions
on the enzyme. These results suggest that excessive cupric ion concentrations could cause various disorders in lipid metabolism. 相似文献
2.
The inhibitory effect of a protein isolated from rat serum on lysosomal acid cholesteryl ester hydrolase (acid CEH; EC.3.1.1.13)
activity was studied. An inhibitor was purified from rat serum following ultracentrifugation and heat treatment using column
chromatography on Sephacryl S-200 and ultrafiltration. The purified inhibitor appeared as a single protein band in sodium
dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. The molecular weight of the inhibitor was 28,000 Daltons as judged
by gel filtration on Sephacryl S-200 and SDS-polyacrylamide gel electrophoresis. The purified inhibitor was shown to be apolipoprotein
A-I (apo A-I), the major apolipoprotein of high-density lipoprotein (HDL), using immunoprecipitation with rat anti-apo A-I
immunoglobulin (Ig)G. Inhibition of acid CEH activity by apo A-I was dependent on the concentration of apo A-I. The values
of Vmax obtained were similar with or without apo A-I. Apo A-I of various other mammalian species, including human, bovine and rabbit,
also inhibited acid CEH activity. Other apolipoproteins, such as apo A-II and apo B, also showed inhibiting activity. On the
other hand, apo A-I had no effect on the activity of other enzymes found in lysosomes, such as cathepsin D, β-glucuronidase
and acid phosphatase. The results suggest that apolipoproteins may play a role in the regulation of hydrolysis of cholesteryl
esters in lipoproteins, that have been transferred to the liver, and that the inhibition of acid CEH activity by apo A-I may
be a characteristic of the lipid-binding protein or be due to changes of the lipid/water interface. 相似文献
3.
An inhibitor of lysosomal acid cholesteryl ester hydrolase (Acid CEH), (EC 3.1.1.13) was found in the cytosolic fraction of
rat liver and various other tissues. The extent of the inhibitory effect was dependent on the concentration of the cytosolic
protein. The Acid CEH inhibitor was heat-labile, nondialyzable, and its inhibitory activity significantly decreased by trypsin
or chymotrypsin digestion, but not by lipase digestion. The inhibitor had no effect on the activity of cathepsin D, β-glucuronidase
and acid phosphatase, which are other enzymes found in lysosomes. The present findings suggest that the inhibitor may be involved
in the regulation of the hydrolysis of cholesteryl esters in lipoproteins that have been transferred into the liver. 相似文献
4.
In the presence of hydroxylamine or ascorbic acid, the inhibitory effects of Cu2+ on lysosomal acid cholesteryl ester hydrolase (acid CEH) partially purified from rat liver were studied.
Hydroxylamine stimulated the inhibition of acid CEH activity by Cu2+ but not that by Zn2+, Fe2+, Co2+, Mn2+, Ca2+, Mg2+ and Hg2+. This Cu2+-dependent inhibition of acid cholesterol ester hydrolase (CEH) activity was completely prevented by ethylenediamine tetraacetic
acid (EDTA), EGTA and o-phenanthroline, a chelator with a stability constant for Cu2+, and also by sulfhydryl agents and cytoplasmic reducing agents such as cysteine, glutathione and mercaptoethanol. In addition,
the stimulative effects of hydroxylamine on Cu2+-dependent inhibition were maintained even after preincubation of Cu2+ with hydroxylamine.
On the other hand, ascorbic acid was found to replace the stimulation by hydroxylamine of the Cu2+-dependent inhibition of acid CEH activity but the effects of ascorbic acid progressively became smaller with prolongation
of the preincubation time. Moreover, addition of chemical radical scavengers to the reaction mixture did not prevent the Cu2+-dependent inhibition of acid CEH activity in the presence of ascorbic acid. These results suggest that Cu2+ causes inhibition of lysosomal acid CEH activity through the formation of Cu1+ in a reductive medium. 相似文献
5.
The diurnal variation in lysosomal acid cholesteryl ester hydrolase (Acid CEH), (EC 3.1.1.13) has been examined in fed, fasted
and adrenalectomized rats. The Acid CEH activity of normal rat liver exhibits a diurnal rhythm with maxima at 06.00 hours
and minima at 18.00 hours, but such a rhythm was not observed in spleen and brain. This rhythm was abolished after fasting
for two days, and the resulting Acid CEH activity remained constant at the minimum level. However, adrenalectomy did not abolish
the diurnal rhythm. These results indicate that the Acid CEH activity varies according to a diurnal rhythm with maxima and
minima separated by approximately 12 hr. Further, it is evident that the appearance of this rhythm is dependent upon dietary,
but not adrenal hormone influence. 相似文献
6.
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. 相似文献
7.
Evidence that cholesteryl ester hydrolase and triglyceride lipase are different enzymes in rat liver
Studies on intracellular cholesteryl ester hydrolase (CEH) and triglyceride lipase (TGL) from rat adipose tissue and adrenal
cortex have suggested that a single protein is responsible for both activities. To determine whether one hepatic protein catalyzes
both reactions, we studied several properties of CEH and TGL in rat liver. During liver perfusion with heparin, perfusate
peaks of TGL and CEH did not consistently coincide, and TGL activity was considerably higher and less heat-stable than that
of CEH. Significant TGL, but not CEH, activity was released during incubation of isolated hepatocytes. Although microsomes
isolated from hepatocytes contained both activities, the specific activities of CEH and TGL in cytosol from hepatocytes were
95% and 3%, respectively, of those found in cytosol from whole liver. Preincubation of liver cytosol with 5 mM Mg2+ decreased CEH, but not TGL, activity. Intracellular CEH and TGL activities were completely separated by prep-disc gel electrophoresis.
Finally, both cytosolic and microsomal TGL, but not CEH, activities were inhibited by antiserum against rat hepatic TGL. We
conclude that extracellular TGL does not have CEH activity and intracellular CEH differs from TGL. 相似文献
8.
The hydrolytic activity usually associated with lysosomes increased in the homogenates and subcellular fractions of rat liver
as a result of essential fatty acid (EFA) deficiency. The proportion of the total (tissue homogenate) activity found in each
subcellular fraction, however, was unchanged by EFA deficiency.
Lysosomes isolated from normal and EFA-deficient rat livers differed significantly in their stability to thermal and osmotic
variations. This suggested that lysosomal membranes, like other membranes, were altered by EFA deficiency.
In spite of increased tissue-bound hydrolytic activity and altered lysosomal membranes, hydrolytic activity of the serum was
not markedly changed in EFA deficiency. These minor changes in hydrolytic activity and in lysosomal membrane stability seemed
insufficient to explain the general lesions of EFA deficiency.
Published with the approval of the Director of The Wisconsin Agricultural Experiment Station. 相似文献
9.
Cholesteryl ester hydrolase (CEH) (EC 3.1.1.13) activity was assayed in the 104,000×g supernatant (S104) of rat and mouse
testes and livers at various temperatures between 27 C and 44 C. The CEH activity in the testis dropped from 44 pmol [4-14C] cholesteryl oleate hydrolyzed/hr/mg protein to 14 pmol hydrolyzed/hr/mg protein (a 68% decrease) between testicular and
abdominal temperatures (32 C and 37 C, respectively) in the rat. This decrease in activity is essentially a reversible phenomenon.
CEH from the testis S104 was stabilized in 10 mM EDTA and was purified by HPLC size exclusion. These steps did not alter the
temperature effect previously noted. The temperature effect on the testicular CEH was demonstrated in vivo by assaying the
enzyme following unilateral cryptorchidism. The HPLC purification yielded 3 peaks of CEH activity from the testicular S104.
The 28,000 MW peak was found to be temperature insensitive while the 70,000 and 420,000 MW peaks were temperature labile.
The liver CEH of both species remained relatively constant over the range 32—37 C. CEH is a potential regulator of both steroidogenesis
and membrane composition in the testis and its temperature lability may suggest a unique regulatory mechanism responsible
for impaired spermatogenesis seen with elevated testicular temperatures. 相似文献
10.
11.
A rat liver cytosolic cholesteryl ester hydrolase (CEH) was purified 12,600-fold by ammonium sulfate precipitation, cation
exchange chromatography and gel permeation high-performance liquid chromatography, with an overall yield of 20%. Its properties
are compared to those of pancreatic CEH, with which it has sometimes been identified. Liver CEH exhibited a single silver
stained band following SDS-polyacrylamide gel electrophoresis (Mr=66 kDa), was activated by 0.5–10 mM taurocholate but was strongly inhibited by higher levels of taurocholate, which activate
pancreatic CEH. Whereas bile salts are known to induce formation of a hexamer of pancreatic CEH, in the current study, 0.5
mM taurocholate dissociated a multimeric form of liver CEH to monomer. Liver CEH did not coelute with pancreatic CEH from
cation exchange and chromatofocusing columns, exhibited no immunoreactivity with anti-rat pancreatic CEH IgG in Western blots,
was not inhibited by anti-rat pancreatic CEH IgG and had a different amino acid composition from pancreatic CEH. In contrast
to liver CEH, which is known to be activated by protein kinases A and C, pancreatic CEH was unaffected by cofactors for protein
kinase A and was inhibited by cofactors for protein kinase C. 相似文献
12.
Kathleen M. Botham 《Lipids》1991,26(11):901-906
An acid cholesteryl ester hydrolase activity associated with a fraction containing mitochondria and lysosomes from rat lactating
mammary glands was found to have a pH optimum of 5.0. Its sedimentation pattern was closely related to that of the lysosomal
enzyme markers acid phosphatase and β-glucuronidase, suggesting that the activity is associated with the lysosomes. The enzyme
was strongly inhibited by Cu2+, but was inhibited little by other divalent metal ions. Acid cholesteryl ester hydrolase activity was almost completely abolished
byp-hydroxymercuribenzoate, but this effect was reversed in the presence of an equimolar concentration of reduced glutathione
(GSH), indicating that the enzyme requires free sulfhydryl groups for activity. These properties are similar to those of acid,
lysosomal cholesteryl ester hydrolases found in other tissues. Acid cholesteryl ester hydrolase activity was 8–14 fold higher
in mammary tissue from lactating as compared to virgin rats. Neutral cholesteryl ester hydrolase activities associated with
the microsomal and cytosolic subcellular fractions were also increased in lactating glands, but to a lesser extent. In addition,
a 2-fold increase in the activities of both the acid and microsomal neutral enzymes was seen during the first few days of
lactation, while the cytosolic neutral activity remained constant. These results suggest that mammary gland cholesteryl ester
hydrolases have a role in the regulation of cholesterol metabolism in mammary cells, and in the provision of cholesterol for
secretion into milk. 相似文献
13.
Cholesteryl ester hydrolase (CEH), triacylglycerol lipase (TGL) and retinyl palmitate hydrolase (RPH) were measured in 104,000
×g supernatants from rat liver under optimal conditions for measurement of cytosolic CEH. Similar levels of hydrolytic activity
were seen with oil droplet dispersions of cholesteryl oleate, trioleoylglycerol and retinyl palmitate. No cytosolic TGL activity
was seen with substrate presented in the triton-albumin emulsion used for measurement of lipoprotein lipase-like TGL associated
with hepatic plasma membrane. Cytosolic CEH, TGL and RPH were differentially partially purified by both ammonium sulfate precipitation
and anion exchange fast protein liquid chromatography (FPLC). Of the three activities, only CEH was stimulated by cholestyramine
feeding and by activators of protein kinases A and C. All three activities were inhibited by alkaline phosphatase treatment,
although to different degrees. It is concluded that these activities are catalyzed by at least three differentially regulated
enzymes with a high degree of specificity for their respective substrates. 相似文献
14.
Kazuo Kasama Katsumi Yoshida Susumu Takeda Ryotaro Tsujimura Shinichi Hasegawa 《Lipids》1976,11(10):718-721
The effect of 4,4′-diethylaminoethoxyhexestrol (DH) on acid esterase in rat liver was studied in vivo and in vitro. The acid
esterase activity in the livers of rats treated with 0.125% DH for 1 week was found to decrease more than 60% as compared
with that in untreated rats. The addition of DH to the incubation medium caused considerable inhibition of the acid esterase
activity in lysosome from untreated rat liver, and the inhibition type appears to be noncompetitive. The acid lipase activity
in rat liver lysosome was also inhibited by DH. Some antihistamic agents and chloroquine also inhibited the acid esterase
activity in rat liver lysosome. 相似文献
15.
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 activityin vitro, but activity returned toward control values, after drug withdrawal. Acyl-CoA:cholesterol acyltransferase (ACAT) was significantly
reduced (P<0.001) by simvastatin (−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. 相似文献
16.
A soluble lysosomal phosphodiesterase in rat liver that hydrolyzes monoacyglycerophosphoryl-glycerophosphorylglycerol (AGPGPGase)
was shown to be distinct from a lysosomal acid phosphodiesterase IV (PDase IV) which catalyzes the hydrolysis of bis(p-nitrophenyl) phosphate. The criteria used to distinguish lysosomal AGPGPGase from PDase IV were: separation on ion exchange
celluloses, dissimilar inhibition patterns and different rates of inactivation on concentration. The lysosomal PDase IV activity
was competitively inhibited by inorganic phosphate with a Ki value of 0.33 mM phosphate and was inhibited by a number of organophosphoryl compounds including AGPGPG, phosphatidylcholine,
phosphatidylinositol, ATP and 4-methylum belliferylpyrophosphate. 相似文献
17.
A study was made of the influence of semisynthetic diets of low and high unsaturation on the fatty acid composition and desaturation-chain
elongation enzymatic activity of the liver microsomal fractions of male Sprague-Dawley rats of different ages. Groups of rats
were fed 5 or 20% coconut oil (CO), or a 5 or 20% mixture of corn and menhaden oils (3∶7) (CME) from weaning to 100 wk of
age. Growth rate and food consumption were measured during this period in which animals were sacrificed at 36, 57, 77 and
100 wk of age. Both the level and composition of the dietary fat supplements produced marked effects on the fatty acid composition
of the liver microsomal lipids. In general, the fatty acid composition of the microsomal fractions reflected that of the dietary
fat and was more unsaturated with the higher level of fat fed. The rate of conversion of linoleic to arachidonic acid in assays
performed in vitro with liver microsomal preparations from animals of the different groups also showed marked differences.
The 6-desaturase-chain elongation activity was higher in the 5% than 20% group and corresponded to the essential fatty acid
(EFA) status of the animals in these groups as represented by the triene-tetraene ratio of the microsomal lipid. The relationship
of the 6-desaturase activity to fatty acid composition of the microsomal lipid indicated that if varied directly with the
level of 20∶3ω9, 18∶1 and 16∶1 and was inhibited by arachidonic acid. The activity of the 6-desaturase enzyme system was lowest
in the liver microsomal fraction obtained from the animals fed the CME diets and appeared to be suppressed by the high levels
of 20∶5 and 22∶6 that accumulated in the microsomal lipid. Accordingly, the levels of arachidonic acid were lower in the microsomal
lipid of these groups than those of the corresponding CO groups in spite of a greater abundance of linoleic acid in the diet.
The data suggest that the activity of the 6-desaturase-chain elongation system is regulated by the fatty acid composition
of the microsomal lipid as influenced by the composition of the dietary fat. 相似文献
18.
Phosphatidate phosphohydrolase (PAPase) activity was measured in lamellar bodies purified from porcine lung tissue. After
repeated freeze-thawing, only a negligible amount of PAPase activity was released into the soluble fractions, whereas there
was release of 2 lysosomal marker enzyme activities, glucosaminidase and β-galactosidase into the soluble fraction. In addition,
a lysosomal-enriched fraction was prepared from adult rat lung tissue by prior treatment of the rats with Triton WR 1339.
Treatment with Triton WR 1339 resulted in the significant shift of the activities of the lysosomal marker enzymes, glucosaminidase
and β-galactosidase, to less dense subcellular fractions. The highest specific activity of PAPase was found in a subcellular
fraction which had a density that was intermediate between that of the mitochondrial and microsomal fractions and the distribution
of PAPase activity was not affected by the prior treatment of the rats with Triton WR 1339. 相似文献
19.
Translocation of long-chain acyl-coenzyme A hydrolase from the microsomal fraction to the cytosolic fraction was promoted
in cell-free extracts of rat liver by palmitic acid, oleic acid, tetradecylthioacetic acid, and tetradecylthiopropionic acid,
and by their CoA esters. The CoA esters were more effective than the non-esterified acids in the translocation of the enzyme.
Treatment of normolipidemic rats with sulfur-substituted non-β-oxidizable fatty acid analogues resulted in a transitory increase
in hepatic concentration of long-chain acyl-CoA. Longer feeding times almost normalized the hepatic long-chain acyl-CoA content.
Microsomal long-chain acyl-CoA hydrolase activity was inhibited, whereas the activity of the cytosolic form was stimulated.
The rise in enzyme activity coincided with a reduction in liver content of triglyceride and an increase in hepatic phospholipid
content. The results suggest that the activity of long-chain acyl-CoA hydrolase in the cytosol may control the amount of acyl-CoA
thioesters in the liver. Esterified and non-esterified fatty acids causedin vitro translocation of phosphatidate phosphohydrolase and cytidine 5′-triphosphate (CTP):phosphocholine cytidylyltransferase from
the cytosolic fraction to the microsomal fraction. However, the translocation of these two enzyme systems was not obtainedin vivo. The activity of phosphatidate phosphohydrolase decreased in microsomal and cytosolic fractions while the activity of cytidylyltransferase
in these fractions increased. The activities of soluble phosphatidate phosphohydrolase and long-chain acyl-CoA hydrolase appeared
to be inversely correlated. The results imply that in cytoplasm, long-chain acyl-CoA hydrolase may compete with the biosynthetic
enzymes for the acyl-CoA substrate, thus influencing the rate of lipid synthesis. The reduced hepatic triglyceride content
observed in tetradecylthioacetic acid-treated rats is probably due to reduced triglyceride synthesis, which is mediated by
an inhibition of phosphatidate phosphohydrolase accompanied with translocation and stimulation of long-chain acyl-CoA hydrolase.
Development of fatty liver as an effect of tetradecylthiopropionic acid is probably due to accelerated triglyceride biosynthesis,
which is mediated by a stimulation of phosphatidate phosphohydrolase and a decrease in cytosolic palmitoyl-CoA hydrolase activity. 相似文献
20.
Transfer-stimulating activity for α-tocopherol and the concentration of α-tocopherol and peroxidized lipids in rat ascites
hepatoma cells were compared with those from normal and regenerating liver.
The ability of supernatants from ascites hepatomas (AH-13, AH-60C, AH-109A) to enhance the transfer of α-tocopherol was much
lower than that from normal livers. The α-tocopherol per mg protein of supernatant from ascites hepatomas was lower than that
from normal liver. Regenerating liver showed almost the same values as normal liver in activity to stimulate the transfer
of α-tocopherol and α-tocopherol content of the supernatant. By gel filtration, about 60% of α-tocopherol in the supernatant
of normal liver was detected in the fractions containing the 30 K protein, which stimulates transfer of α-tocopherol between
membranes, whereas no significant amount of α-tocopherol was detected in 30 K protein fractions of AH-60C supernatant. Little
stimulating activity for α-tocopherol transfer was detected in AH-60C, AH-109A and AH-13.
All ascites hepatomas tested contained less arachidonic acid and docosahexaenoic acid than normal and regenerating liver.
An absorption peak with maximum intensity at 233 nm, which is due to conjugated dienes, was observed in UV-absorption spectra
of ascites hepatoma total lipids, indicating that peroxidized lipids accumulate in these cells. With normal and regenerating
liver, no significant peak due to conjugated dienes was detected. 相似文献