Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.1.34 (lipoprotein lipase)
 7,025 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

This paper shows that the palmitoyl-CoA hydrolase activity of postheparin serum of the rat is mainly derived from the liver. The identity of this activity with the heparin-releasable hepatic triacylglycerol hydrolase activity is established. The consequences of the different substrate specificities of the hepatic and extrahepatic enzymes for the measurement of the overall postheparin serum lipase activity are discussed. Treatment of the rats with either a corticosteroid or with streptozotocin was found to lower the lipolytic activity from the liver and to enhance the extrahepatic activity. Also in human postheparin serum, palmitoyl-CoA hydrolase activity is shown to behave identical with hepatic triacylglycerol hydrolase activity. The possible function of the liver in the serum triacylglycerol metabolism is discussed in connection with the proposed mechanism for the role of extrahepatic lipoprotein lipase in atherogenesis.
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PMID:On hepatic and extrahepatic postheparin serum lipase activities and the influence of experimental hypercortisolism and diabetes on these activities. 12 97

These studies demonstrate that canine liver synthesizes a TGH activated by C-I but not by C-II. This TGH has properties similar to lipoprotein lipase C-I isolated from postheparin plasma of human subjects, but differs from a previously reported liver triglyceride-lipase or protamine insensitive-lipase in its sensitivity to NaCl and protamine sulfate, as well as in its requirement for a serum cofactor, C-I. These data suggest the possiblity that, in dogs, liver is a source of plasma LPLC-I.
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PMID:Characterization of a triglyceride hydrolase secreted by canine liver maintained in vitro. 17 81

The function of the hepatic triglyceride lipase (H-TGL) is not yet clear. The purpose of the present study was to investigate the possible hormonal regulation of H-TGL. Postheparin plasma was obtained 3 min after the intravenous injection of 50 U/250 g body weight of heparin into male Wistar rats. The lipase activities were measured using substrate containing [14C] triolein emulsified with gum arabic and were expressed in mumoles of free fatty acid released/ml/hour (mean +/- SD). H-TGL was the lipase activity remaining after inhibition of lipoprotein lipase (LPL) by 1.0 M NaCl. Diabetic rats were prepared by intravenous injection of streptozotocin (STZ), 65 mg/kg body weight. The contributions of H-TGL and LPL to the total plasma triacylglycerol hydrolase (TGH) activity depend on the amount of heparin injected and the time of blood withdrawal after heparin injection. H-TGL was maximally released at higher heparin (50 U/250 g body weight) concentrations, compared to LPL which was maximally released at lower heparin (5 U/250 g body weight) concentrations. H-TGL was significantly higher at 3 min after the injection of 50 U of heparin/250 g body weight than at 20 min. Twenty-four-hour fasting produced a significant fall in H-TGL compared to H-TGL in fed rats. Total TGH was significantly lower in diabetic rats 3 days after STZ injection. In diabetic rats 3, 5, and 7 days after STZ injection, H-TGL were significantly lower than those in control rats. H-TGL and H-TGL/total TGH were 9.49 +/- 0.99 and 0.551 +/- 0.071, respectively, in rats 3 days after STZ injection, compared to H-TGL (13.46 +/- 0.69) and H-TGL/total TGH (0.739 +/- 0.052) in control nondiabetic rats. When diabetic rats were treated with insulin, total TGH (14.37 +/- 3.01) and H-TGL (6.77 +/- 4.12) rose to 25.16 +/- 1.02 (total TGH) and 16.49 +/- 1.13 (H-TGL), that were comparable to activities in control nondiabetic rats. Separation of H-TGL and LPL was performed using heparin-Sepharose affinity chromatography of postheparin plasma. The enzyme activity of peak I from STZ rats, which is eluted by 0.72 M NaCl-Veronal buffer, pH 7.4 and corresponds to H-TGL, was approximately half the activity from control rats. TGH released by heparin from isolated rat liver parenchymal cells was investigated. The enzyme activites released from isolated liver parenchymal cells prepared from STZ rats was approximately half that from control rats. The role of insulin in the regulation of LPL has been well documented. Our findings suggest that H-TGL also is under hormonal regulation by insulin in rats.
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PMID:The effects of streptozotocin diabetes on hepatic triglyceride lipase activity in the rat. 75 24

In rats fed a fish oil-enriched diet, plasma triacylglycerols were lowered 51%. At the same time there was a mean 45% reduction in Mg2+-dependent phosphatidate phosphohydrolase activity in liver microsomes and a mean 20% decrease in microsomal triacylglycerol (neutral) and diacylglycerol hydrolase activities, but not of diacylglycerol acyltransferase. These observations support the hypothesis that decreases in the activities of phosphatidate phosphohydrolase and of both lipases are involved in the expression of the inhibitory effects of fish oil feeding on hepatic lipoprotein triacylglycerol secretion. Conversely, the feeding of a sucrose-enriched diet resulted in a mean 39% rise in plasma triacylglycerols, a 19% increase in triacylglycerol hydrolase and a mean 45% increase in Mg2+-dependent microsomal phosphohydrolase activity. The effects of the two nutritional interventions on phosphatidate phosphohydrolase activity confirm a key function for this enzyme in triacylglycerol formation.
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PMID:Comparative effects of dietary fish oil and carbohydrate on plasma lipids and hepatic activities of phosphatidate phosphohydrolase, diacylglycerol acyltransferase and neutral lipase activities in the rat. 282 8

Primary cultures of chromaffin cells from bovine adrenal medullae were used as a model to study lipolytic events during stimulus-secretion coupling. It has been shown that chromaffin cells liberate arachidonic acid in addition to their main secretion product, the catecholamines. To understand more about the mechanism of arachidonic acid liberation, chromaffin cells were labeled with radioactive arachidonic acid, stimulated, and then analyzed for changes in lipid composition. After stimulation with 10(-4) M acetylcholine, the radioactivity of triacylglycerols decreased to the same extent that the free arachidonic acid level rose. This finding suggests that in bovine chromaffin cells a stimulation-dependent triacylglycerol lipase (triacylglycerol hydrolase; EC 3.1.1.3) is involved in arachidonic acid liberation. Further work was performed on detection, characterization, and isolation of this enzyme. Triacylglycerol lipase activity was found in whole cell homogenates and in plasma membrane fractions isolated from adrenal medullary tissue. The plasma membrane lipase showed a pH optimum of 4.3. The apparent Michaelis constant was determined as 3.3 x 10(-4) mol/L. Ca2+ did not influence the enzymatic activity. To differentiate the plasma membrane triacylglycerol lipase from the previously described plasma membrane diacylglycerol lipase of chromaffin cells, the influence of RG 80267, a specific diacylglycerol lipase inhibitor, was examined. RG 80267 (50 microM) inhibited the triacylglycerol lipase by only 24%, although diacylglycerol lipase was totally inhibited with only 20 microM RG 80267. The pH optimum of homogenate lipase was broad, lying between 4 and 7. Starting from the soluble fraction of whole cell homogenates, the triacylglycerol lipase was partially purified by ultracentrifugation and size-exclusion chromatography.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Characterization of a triacylglycerol lipase that liberates arachidonic acid from bovine chromaffin cells during secretion. 841 52

Triacylglycerol hydrolase activities were characterised in homogenates, cytosol, and microvillous membranes (MVM) of human placenta. Homogenates of placenta exhibited three distinct triacylyglycerol hydrolase activities with pH optima 4.5, 6.0 and 8. 0. On further fractionation, placental cytosol exhibited both acid cholesterol ester hydrolase (pH 4.5) and hormone sensitive lipase (pH 6.0) activities, whereas purified placental MVM exhibited two distinct triacylyglycerol hydrolase activities; a minor activity at pH 8.0 and a second major activity at pH 6.0. Triacylglycerol hydrolase activity at pH 8.0 of MVM appeared to be lipoprotein lipase (consistent with criteria such as serum stimulation and salt inhibition), whereas at pH 6.0 the activity was unique in that it was almost abolished by serum, but was not affected by high NaCl concentrations. Our data, for the first time, demonstrate that human placental MVM, in addition to lipoprotein lipase, contain a newly identified triacylglycerol hydrolase activity at pH 6.0.
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PMID:Characterisation of triacylglycerol hydrolase activities in human placenta. 979 1

Watanabe heritable hyperlipidemic (WHHL) rabbit is an animal model for human familial hypercholesterolemia. Recently, we segregated a new mutant of WHHL rabbits with plasma levels of triglycerides (TG) >500 mg/dl (designated as TGH-WHHL). To investigate the underlying mechanisms for hypertriglyceridemia, we compared TGH-WHHL with WHHL rabbits with lower plasma TG levels (<250 mg/dl, designated as TGL-WHHL). A Triton WR-1339 injection experiment revealed that TGH-WHHL rabbits had increased secretion and decreased clearance of TG-rich lipoproteins. Furthermore, TGH-WHHL rabbits had lower a post-heparin activity of lipoprotein lipase and a higher cholesterol ester transfer protein activity than TGL-WHHL rabbits. Cultured hepatocytes isolated from TGH-WHHL rabbits showed a higher secretion rate of TG and cholesterol than those of TGL-WHHL rabbits. In addition, TGH-WHHL rabbits exhibited marked insulin resistance. These data suggest that hypertriglyceridemia exhibited by WHHL rabbits is caused by both increased production and impaired catabolism of TG-rich lipoproteins and associated with insulin resistance.
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PMID:Hypertriglyceridemia in Watanabe heritable hyperlipidemic rabbits was associated with increased production and reduced catabolism of very-low-density lipoproteins. 1995 43

Infection and inflammation induce important changes in lipid metabolism, which result in increased free fatty acids and triacylglycerol in plasma and altered high density lipoprotein (HDL) metabolism. Our aim was to elucidate whether hepatic lipid droplets (LDs) are involved in the adaptations of lipid metabolism to endotoxemia. We characterized the lipid content and several enzymatic activities in subcellular fractions and subpopulations of LDs from livers of mice 24h after lipopolysaccharide (LPS) treatment and analyzed the expression of key genes involved in lipid management. Endotoxemic mice showed lower lipid content in LDs with decreased molar fraction of cholesteryl ester and higher diacylglycerol/triacylglycerol ratio as compared to their controls. They also showed a decrease in cytosolic triacylglycerol hydrolase activity, specifically in dense LDs, and in microsomal and cytosolic diacylglycerol hydrolase activity; concomitantly neutral lipid biosynthetic capacity and triacylglycerol levels in plasma lipoproteins increased. Together with the overexpression of genes involved in lipogenesis and HDL formation our results suggest that altered hepatic management of LD lipids in LPS-treated mice might be related to the channeled mobilization of triacylglycerol for very low density lipoprotein assembly and to the induction of cholesterol export.
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PMID:Involvement of lipid droplets in hepatic responses to lipopolysaccharide treatment in mice. 2366 17