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)

The binding of lipoprotein lipase to a fluorescently labelled apolipoprotein C-II in free solution has been followed by measuring fluorescence anisotropy. The formation of a weak, binary complex in which a single apolipoprotein C-II molecule associates non-cooperatively with each subunit of the dimeric enzyme was observed. The dissociation constant for this complex in 0.05 M NaCl is 0.2 X 10(-6) M and it is weakened markedly by raising the salt concentration and by the binding of heparin to the enzyme. The assembly of the same protein-protein complex on the surface of glycerol trioleate globules has been monitored by steady-state and pre-steady-state kinetics. In these circumstances the lipoprotein lipase-apolipoprotein C-II interaction is much tighter (Kd = (7-10) X 10(-9) M) and is insensitive to salt and heparin. The mechanism of activation of the enzyme at low concentrations of apolipoprotein C-II is described by a kinetic model in which apolipoprotein C-II binds preferentially to the form of the enzyme which is associated with the triacylglycerol substrate. This preference leads to a stabilization of the enzyme-substrate complex, thus reducing the apparent Ks.
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PMID:The mechanism of activation of lipoprotein lipase by apolipoprotein C-II. The formation of a protein-protein complex in free solution and at a triacylglycerol/water interface. 397 Sep 43

Lipoprotein lipase has been shown to bind to, be internalized by, and perhaps be transferred through, a variety of cells. These processes may involve a heparin-like cell-surface receptor and passage through acidified cell compartments. We have therefore studied effects of low pH on the binding of the lipase to heparin and on its catalytic activity. The rate of inactivation of the lipase in solution was found to increase as the pH was lowered. Addition of heparin stabilized the enzyme. Binding of active lipoprotein lipase to heparin-Sepharose could be demonstrated at pH down to 6.5. At pH below 6, binding could not be studied directly because the lipase was too unstable in solution. Lipase bound to heparin-Sepharose could, however, be exposed to pH 4.5 at 10 degrees C with little loss of activity. Binding to heparin-Sepharose also stabilized under physiological conditions (37 degrees C, 0.15 M-NaCl, pH 5.5-7.4). Catalytically inactive lipoprotein lipase retained the ability to bind to heparin-Sepharose. Higher concentrations of salt were needed to displace both active and inactive lipase from heparin-Sepharose at lower pH, indicating that the affinity increased as pH was lowered. The inactive lipase was, however, displaced by lower concentrations of salt than was active lipase.
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PMID:Binding of active and inactive forms of lipoprotein lipase to heparin. Effects of pH. 399 67

We have described methodology for the isolation and quantitation of glycosaminoglycans present in human plasma. Plasma glycosaminoglycans can be quantitatively adsorbed on a DEAE-Sephacel ion exchanger and eluted with a salt gradient as two groups: a low-charge fraction and a high-charge fraction. The low-charge fraction consists of chondroitin sulfate with a low sulfate content and the high-charge fraction consists of heparan sulfate, chondroitin sulfate, and keratan sulfate (type I). We have determined the plasma concentration of each of these glycosaminoglycans in six normal human subjects. We have established that none of the glycosaminoglycans in plasma are covalently linked to plasma proteins. All are isolated as complexes with plasma proteins in noncovalent linkages. The glycosaminoglycans in the low-charge fraction are bound with high affinity to a single plasma glycoprotein by a lectin-type bond that can be disrupted by a simple glycoside. The high-charge fraction contains three major proteins and several minor proteins associated with the glycosaminoglycans by both lectin-type and ionic bonding. The plasma proteins associated with glycosaminoglycans represent less than 0.5% of the total plasma proteins. Little is known about the physiologic role of the plasma glycosaminoglycans as components of metabolic processes. Because glycosaminoglycans have been implicated in lipid metabolism and atherosclerosis, we tested all of these compounds, isolated in free form, on the in vitro hydrolysis of triglycerides by lipoprotein lipase. Plasma heparan sulfate stimulated the rate of this reaction severalfold. All other plasma glycosaminoglycans were inactive. Thus, plasma heparan sulfate may play an important role in plasma lipoprotein metabolism.
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PMID:Isolation and characterization of glycosaminoglycans in human plasma. 405 61

The alkaline, heparin-releasable lipoprotein lipase (LPL) activity of isolated, perfused rat hearts was compared with the residual neutral lipase (NL) activity detectable in the post nuclear supernatant (PNS) from a tissue homogenate. Both enzyme activities were increased by serum, heparin and apolipoprotein CII, inhibited by high salt concentrations and by immunotitration with an anti-LPL gamma-globulin fraction. Protamine sulphate from saline liver inhibited LPL activity and the NL activity only in the absence of serum. Incubation of the PNS NL under classic conditions of hormonal stimulation (by phosphorylation) did not alter its activity and upon short-term preperfusion of the hearts with norepinephrine and glucagon also unchanged LPL and NL activities were measured. Our experiments are indicative of a possible similarity between vascular LPL and tissue NL and show that the lipase activities are not sensitive towards hormonal stimulation.
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PMID:Comparison of heparin-releasable lipase and tissue neutral lipase activity of rat heart. 667 39

This paper demonstrates a striking difference between the effects of salt and pH on the activity of lipoprotein lipase against two different substrates: Intralipid and bovine milk fat droplets. With the former substrate 1 M NaCl caused only a slight reduction in enzyme activity and the stimulation by apolipoprotein C-II was the same from 0.1 to 1.1 M NaCl. In contrast, 0.5 M or more NaCl virtually abolished the enzyme activity in the milk system. In this system the salt also abolished binding of the enzyme to the lipid droplets, whereas in the Intralipid system most of the enzyme remained bound even at 1 M NaCl. A similar picture was obtained with respect to effects of pH. In the milk system the activity decreased sharply at pH values above 8.5, whereas in the Intralipid system it continues to rise to pH 10, and the stimulation by activator protein is the same at all pH values. Correlating with this, the binding of the enzyme to the lipid droplets was highly dependent on pH values in the milk systems, with optimum binding around pH 8, whereas in the Intralipid system most of the enzyme remained bound to the lipid droplets at all pH values. These studies demonstrate that apolipoprotein C-II can activate lipoprotein lipase at a wide range of salt concentrations and of pH. They suggest that the well-known effects of high salt concentrations and of high pH to decrease lipoprotein lipase activity are exerted primarily on the enzyme itself.
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PMID:The effects of pH and salt on the lipid binding and enzyme activity of lipoprotein lipase. 683 Aug 43

The interactions of bovine milk lipoprotein lipase (triacylglycero-protein acylhydrolase, EC 3.1.1.34) with the glycosaminoglycans heparin and heparan sulphate were investigated using the technique of fluorescence polarization spectroscopy. The type of complex formed with the enzyme depends on the chain length of the heparin. In 0.05 M NaCl and when the heparin was in molar excess, one heparin chain of Mr 10000-18400 formed a very stable complex with the dimeric protein molecule (the 1:1 complex). With excess protein, weaker interactions produced complexes with higher molecular weights. These two classes of complex were also detected with shorter heparins (Mr 6600-8000), although in these circumstances the more stable complex possessed a heparin:protein dimer ratio of 2:1. In higher salt (0.2 M NaCl) and lower heparin concentrations (less than 6 . 10(-8) M) the weaker class of compound was undetectable and Kd values of 4 . 10(-8) M and 6 . 10(-9) M were assigned to the 2:1 and 1:1 complexes, respectively. Heparan sulphate of Mr 17000 could only form one class of complex. This had a 1:1 stoichiometry and with Kd values of 3 . 10(-8) M and 1.6 . 10(-7) M at 0.05 and 0.2 M NaCl, respectively. The results could be explained if there is a distinct binding region for glycosaminoglycans on each subunit of the dimeric enzyme and a single heparin chain of Mr greater than 10000 can satisfy both sites to form a 1:1 complex. Smaller heparin chains are unable to span the sites and, in order to occupy them, two chains must interact with each enzyme molecule.
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PMID:The effect of the chain length of heparin on its interaction with lipoprotein lipase. 688 75

Human monocyte-derived macrophages in culture produced lipoprotein lipase. Although freshly isolated blood monocytes did not secrete much lipase activity, 1 d in culture was sufficient to trigger measureable enzyme production. During 3 wk in culture, maximal activity was attained after 7 d. At all times, the culture medium contained more enzyme activity than did a serum-heparin eluate or a detergent extract of the cell layer. The lipase activity was stimulated by serum and was inhibited by preincubation with antiserum to bovine lipoprotein lipase or when assayed at a high salt concentration. Furthermore, the enzyme bound to a heparin-Sepharose affinity column at physiological ionic strength. Cells cultured from a subject with primary lipoprotein lipase deficiency secreted no detectable enzyme. Since macrophages are prominent components of atherosclerotic lesions in man, their ability to synthesize and secrete lipoprotein lipase may be important to atherogenesis.
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PMID:Lipoprotein lipase secretion by human monocyte-derived macrophages. 705 57

Although human milk generally contains higher levels of enzymes than bovine milk, little definitive information is available concerning their role or significance. The enzyme levels in human milk as compared to bovine milk and levels in human colostrum versus normal milk are summarized. The few most widely studied human milk enzymes are discussed in more detail. Evidence is presented to support the views that 1) lipoprotein lipase and ribonuclease are probably spilled into the milk from the blood; 2) lysozyme is spilled from the secretory epithelial cells; 3) lactate and malate dehydrogenases, glucose-6-phosphate dehydrogenase, and lactose synthetase are synthesized in the mammary gland in response to hormonal stimuli; and 4) bile salt stimulated lipase, diastase, protease, and lysozyme are present in sufficient quantities to aid infants in growth and nutrition. Consideration must be given to standardizing the various enzyme assay procedures and activity units so that meaningful comparisons between various studies could be made.
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PMID:Role and significance of enzymes in human milk. 740 88

Heparin-derived deca- and octa-saccharides were subjected to affinity chromatography on lipoprotein lipase-Sepharose and the fractions eluted at high salt concentration were analysed by strong-anion-exchange chromatography. Two high-affinity decasaccharides were isolated and the structure determined by one- and two-dimensional 1H-n.m.r. spectroscopy. The affinities of 3H-labelled low-molecular-mass heparin and size-fractionated deca-, octa-, and hexa-saccharides for lipoprotein lipase immobilized on microtitre plates were determined from saturation curves. From competition experiments the affinities of unlabelled heparins and pure deca- and hexa-saccharide fragments were determined. The binding was size- and charge-dependent, but structural dependency was also indicated. Thus substitution of a 2-O-sulphated L-iduronic acid with D-glucuronic acid was less important than the sulphation pattern of the D-glucosamine residue for affinity for lipoprotein lipase. Heparin inhibits binding of lipoprotein lipase to alpha 2-macroglobulin-receptor/low-density-lipoprotein receptor-related protein. The effects of size, charge and structure for this inhibition were studied. The ability of the heparin fragments to inhibit binding correlated with their affinity for lipoprotein lipase. This indicates that the inhibition of the binding of lipoprotein lipase to alpha 2-macroglobulin-receptor/low-density-lipoprotein receptor-related protein by heparin is exclusively mediated by binding of heparin to lipoprotein lipase.
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PMID:Structure of heparin fragments with high affinity for lipoprotein lipase and inhibition of lipoprotein lipase binding to alpha 2-macroglobulin-receptor/low-density-lipoprotein-receptor-related protein by heparin fragments. 771 77

Methods available for measurement of plasma lipoprotein-cholesterol concentrations and activities of lipoprotein lipase, hepatic lipase, lecithin:cholesterol acyl transferase (LCAT), and cholesteryl ester transfer protein were adapted for use in cats. A combined ultracentrifugation/precipitation procedure was used to isolate very low-density lipoproteins (VLDL), then to separate low-density lipoproteins (LDL) from high-density lipoproteins (HDL). The reagent used, 92 mM heparin-manganese chloride, provided complete precipitation of LDL with only trace and insignificant contamination by HDL. Efforts to selectively measure lipoprotein lipase activity in plasma, collected after IV injection of heparin, by inhibiting hepatic lipase with sodium dodecyl sulfate were unsuccessful, and the activity of this enzyme was calculated as the difference between total and hepatic lipase activities. The latter was measured in the presence of high salt concentration to inhibit lipoprotein lipase. Cholesterol esterifying activity was identified in feline plasma and was typical of LCAT, in that it was dependent on apolipoprotein A-I as a cofactor. The intra-assay and interassay coefficients of variation for measurement of lipoprotein lipase, hepatic lipase, and LCAT activities were 18.4, 4.6, and 7.2%, and 20.4, 10.7, and 5.3%, respectively. Appreciable cholesteryl ester transfer protein activity was not detected in either undiluted or diluted plasma. These methods were subsequently used to investigate the effects of pregnancy and lactation on lipoprotein metabolism in a group of 10 queens. Plasma concentrations of cholesterol and triglycerides were unaltered during pregnancy, but the concentrations of VLDL-cholesterol increased and those of HDL-cholesterol decreased.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Development of methods for analyzing plasma lipoprotein concentrations and associated enzyme activities and their use to measure the effects of pregnancy and lactation in cats. 777 94


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