Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.1.1.34 (lipoprotein lipase)
7,025 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

It has been postulated that the diacylglycerol lipase pathway is a predominant source of the free arachidonic acid which is released from phospholipids upon the exposure of human platelets to thrombin. The amount of released arachidonic acid and other fatty acids in thrombin-stimulated platelets was determined in the presence of BW755C, the cyclooxygenase/lipoxygenase inhibitor, and in relation to phosphatidylinositol degradation and phosphatidic acid formation. A stearic acid:arachidonic acid molar ratio approaching unity would be expected in the free fatty acid fraction if the latter pathway were a major source of released arachidonic acid. Our results indicate that the diacylglycerol lipase pathway contributes a maximum of 3-4 nmol of arachidonic acid/2 X 10(9) platelets or 12-15% of the total arachidonic acid released (25.8 nmol/2 X 10(9) platelets) upon exposure to thrombin (2 units/ml) for 4 min. Trifluoperazine inhibited most of the thrombin-dependent free arachidonic acid release but only 15% of the absolute loss of arachidonic acid from phosphatidylinositol. Therefore, we conclude that the diacylglycerol lipase pathway represents only a minor source of the free arachidonic acid that is released upon thrombin stimulation of human platelets.
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PMID:Diacylglycerol lipase pathway is a minor source of released arachidonic acid in thrombin-stimulated human platelets. 308 Oct 1

Phospholipase C (PLC) and diacylglycerol lipase (DGL) activities were found in guinea pig platelet microsome preparations. No phospholipase A2 (PLA2) activity was detected. RHC 80267 (1,6-di (0-(carbamoyl) cyclohexanone oxime)hexane) inhibited DGL activity (IC50 = 4 uM) from guinea pig platelet microsomes but had no effect on PLC. RHC 80267 inhibited platelet aggregation (IC50 = 11 uM), release of arachidonic acid (AA), its metabolites, and ATP (IC50 = 4.5 uM) when guinea pig platelets were challenged with a low concentration of thrombin. We propose that PLC-DGL is an important enzymatic pathway for the release of AA in guinea pig platelets.
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PMID:Inhibition of the effects of thrombin on guinea pig platelets by the diacylglycerol lipase inhibitor RHC 80267. 309 68

GTP or GTP gamma S alone caused low but significant liberation of arachidonic acid in saponin-permeabilized human platelets but not in intact platelets. GTP or GTP gamma S also enhanced thrombin-induced [3H]arachidonic acid release in permeabilized platelets. Inhibitors of the phospholipase C (neomycin)/diacylglycerol lipase (RHC 80267) pathway for arachidonate liberation did not reduce the [3H]arachidonic acid release. The loss of [3H]arachidonate radioactivity from phosphatidylcholine was almost equivalent to the increase in released [3H]arachidonic acid, suggesting the hydrolysis of phosphatidylcholine by phospholipase A2. The effect of GTP gamma S was greater at lower Ca2+ concentrations. These data indicate that the release of arachidonic acid by phospholipase A2 in saponin-treated platelets may be linked to a GTP-binding protein.
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PMID:Guanine nucleotides stimulate arachidonic acid release by phospholipase A2 in saponin-permeabilized human platelets. 311 31

The in vitro effect of apolipoprotein C-II (apo C-II) on the apolipoprotein C-III (apo C-III) induced activation of bovine milk lipoprotein lipase (LPL) was studied in vitro using a synthetic substrate. Apo C-III effectively inhibited, in a dose-dependent manner, the activation of lipoprotein lipase induced by apo C-II. A 3-fold molar apo C-III excess decreased the lipoprotein lipase activity by 25%. Thrombin cleavage of apo C-III produced two fragments: only fragment 41-79 retained the inhibitory activity and was equipotent to native apo C-III1 on a molar basis. Neither displacement of apo C-II from the substrate, as determined using 125I-labeled apo C-II, nor the charge carried by sialic residues of apo C-III, as demonstrated in experiments performed after neuraminidase treatment, accounted for this effect. I speculate that apo C-III may act by inhibiting the apo C-II-LPL interaction.
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PMID:Activation of lipoprotein lipase by apolipoprotein C-II is modulated by the COOH terminal region of apolipoprotein C-III. 344 10

The possible role of Mg in the pathogenesis of vascular disease has recently received increasing attention. Accumulating evidence indicates that Mg strongly influences vascular tone and responsiveness to pressor agents and that Mg deficiency may be associated with an increased risk of hypertension. Moreover, experimental Mg deficiency produces vascular lesions with calcifications while increasing the dietary intake of Mg has been shown to prevent atheroma and thrombotic complications. The modifications of lipid metabolism during experimental Mg deficiency have been recently characterized. Severe Mg deficiency in weanling rats produces a marked hypertriglyceridemia and a decrease in the percentage of cholesterol transported by high-density lipoprotein. The decreased clearance of circulating triglycerides appears to be the major mechanism contributing to hyperlipemia. The same animals were found to have a reduced insulin response after intravenous glucose challenge and a slight reduction in heparin release lipoprotein lipase. A marked reduction in plasma activity of LCAT and a significant decrease in esterified/total plasma cholesterol ratio have also been reported. Severe Mg deficiency in weanling rats produces marked changes in the fatty acid pattern of total plasma lipids, as shown by decreased levels of stearic acid, increased of oleic acid and linoleic acid, and decreased levels of arachidonic acid. Platelets from Mg-deficient rats become more sensitive to thrombin. Such an increased sensitivity of platelets may in turn play an important role in initiating the vascular lesion as well as in thrombotic complications. In view of these experimental data in animal models, more work seems necessary in man to assess the effect of Mg on lipid metabolism and vascular disease.
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PMID:Magnesium, lipids and vascular diseases. Experimental evidence in animal models. 352 56

Lipoprotein lipases from human, bovine or guinea-pig milk were purified, judged for domain relationships by characterization of sites sensitive to proteases, and structurally compared. The subunit of human lipoprotein lipase migrated slightly slower than those of bovine or guinea-pig lipoprotein lipases on sodium dodecyl sulfate/polyacrylamide gel electrophoresis. Bovine lipoprotein lipase is known to be a dimer of two non-covalently linked subunits of equal size, and the lipases from all three sources now yielded homogeneous N-terminal amino acid sequences (followed for 15-27 residues). The results indicate that the two subunits are identical. Bovine lipoprotein lipase had two additional N-terminal residues, Asp-Arg, compared to the human and guinea-pig enzymes, and the next two positions revealed residue differences, but further on homologies were extensive between all three enzymes as far as presently traced. Exposure of bovine lipoprotein lipase to trypsin led to production of three fragments (T1, T2a, and T2b), suggesting cleavage at exposed segments delineating domain borders. Time studies gave no evidence for precursor-product relationships between the fragments, and prolonged digestion did not lead to further cleavage. Fragments T2a and T2b had the same N-terminal sequence as intact lipase. Fragment T1 revealed a new sequence, and represents the C-terminal half of the molecule. Plasmin caused a similar cleavage as trypsin, whereas thrombin, factor Xa, and tissue plasminogen activator did not cleave the enzyme. Chymotrypsin cleaved off a relatively small fragment from the C-terminal of the molecule, after which exposure to trypsin still resulted in cleavage at the same sites as in intact lipase. Tryptic cleavage of guinea-pig lipoprotein lipase yielded two fragments. One had a similar size as bovine fragment T2b; the other had a similar size as bovine fragment T1 and an N-terminal sequence homologous with that of T1. Thus, trypsin recognizes the same unique site in guinea-pig lipoprotein lipase as in the bovine enzyme. This confirms the conclusion that this segment is the border between two domains in the subunit. The binding site for heparin was retained after both tryptic and chymotryptic cleavages and was identified as localized in the C-terminal part of the molecule.
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PMID:Lipoprotein lipases from cow, guinea-pig and man. Structural characterization and identification of protease-sensitive internal regions. 353 11

Rabbit thoracic aorta segments were treated with either proteoglycan-degrading enzymes or with glycosaminoglycan-binding proteins to examine the nature of the endothelial and subendothelial binding sites of 125I-thrombin. Treatment (5-30 min) with enzymes (heparitinase, chondroitinases AC or ABC) caused a decrease in 125I-thrombin binding by the endothelium (30-70%) and by the subendothelial (intima-media) layer (20-50%); a low-specificity protease destroyed endothelial binding almost entirely and reduced binding to the subendothelium by approximately 60% over a similar period. Of the glycosaminoglycan-binding proteins, pretreatment of the aorta wall with protamine caused a 30% decrease in thrombin binding to the endothelium whereas lipoprotein lipase (present during 125I-thrombin uptake) decreased binding by up to 40%. Pretreatment with antithrombin III did not significantly affect binding of either 125I-thrombin or 125I-FPR-inactivated thrombin. In contrast to thrombin, 125I-antithrombin III was not readily uptaken by the aorta segments. These observations indicate that, whereas the minimal binding by 125I-antithrombin III probably does not involve endothelial proteoglycan, a strong case can be made for endothelial and subendothelial proteoglycan binding sites for thrombin.
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PMID:A role for pericellular proteoglycan in the binding of thrombin or antithrombin III by the blood vessel endothelium? The effects of proteoglycan-degrading enzymes and glycosaminoglycan-binding proteins on 125I-thrombin binding by the rabbit thoracic aorta in vitro. 402 34

The lipolytic and anticoagulant actions of a 4000 dalton low molecular weight (LMW) heparin were compared with unfractionated mucosal heparin after intravenous and various subcutaneous doses in man. I.v. injection of 100 USP units/kg body weight lipoprotein lipase (LPL) activity, and inhibition of factor Xa decreased with a half life twice as long after LMW heparin compared to normal heparin (p less than 0.05). There were no differences in half lives for HTGL activity, thrombin inhibition and on aPTT. The area under the activity time curve (AUC) of LPL and factor Xa was double with LMW heparin (p less than 0.05). S.c. administration showed that the AUC of LMW heparin on the factor Xa inhibition was 10 times larger compared to normal heparin. LPL activity was released comparable to normal heparin. The effects on HTGL were three times larger compared to normal heparin. There were no differences in half lives. The data show that in contrast to normal heparin LMW heparin is rapidly and completely absorbed from the subcutaneous depots. The pharmacodynamic data of LPL activity and factor Xa inhibition suggest similar release mechanisms.
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PMID:Anticoagulant and lipolytic effects of a low molecular weight heparin fraction. 408 6

Human platelets prelabeled with arachidonate exhibited a rapid and transient rise in arachidonoyl monoglyceride in addition to arachidonoyl diglyceride following thrombin stimulation. Substantial release of arachidonate and its metabolites also occurred at the early phase. Preincubation of labeled platelets with RHC 80267, a potent inhibitor of diglyceride lipase, prior to thrombin stimulation abolished the transient rise in monoglyceride but not the increase in diglyceride and the release of arachidonate and its metabolites. These results suggest that diglyceride does metabolize to monoglyceride and release arachidonate in intact platelets. However, the diglyceride/monoglyceride lipases pathway does not appear to be essential in releasing arachidonate during thrombin stimulation.
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PMID:Diglyceride/monoglyceride lipases pathway is not essential for arachidonate release in thrombin-activated human platelets. 630 50

RHC 80267 inhibits diglyceride lipase activity in microsomes from canine platelets (1). Chau and Tai (2) reported that RHC 80267 prevents the transient accumulation of monoglyceride in thrombin-stimulated human platelets, while leaving arachidonate release unimpaired. In contrast, we find that while the drug inhibits both diglyceride lipase (I50 = 15 microM) and monoglyceride lipase (I50 = 11 microM) activities in platelet microsomes, it is ineffective when added to intact platelets. The transient intermediates in the diglyceride lipase pathway, 1,2-diglyceride and 2-monoglyceride, both accumulated after thrombin stimulation of intact platelets treated with RHC 80267, and arachidonate release was not inhibited. We conclude that RHC 80267 cannot be used to evaluate the diglyceride lipase pathway in intact platelets.
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PMID:RHC 80267 does not inhibit the diglyceride lipase pathway in intact platelets. 641 55


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