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)

Vitellogenin isolated from laying-hen plasma strongly inhibited chicken adipose-tissue lipoprotein lipase in vitro, but inhibition was reduced or prevented by Ca2+ and Mg2+ ions and by partial dephosphorylation. Plasma from blood collected from laying hens using EDTA as anticoagulant was a potent inhibitor of lipoprotein lipase, but serum from laying hen blood caused inhibition only when dilute or after addition of EDTA. Heparin reduced or abolished the inhibition of lipoprotein lipase by plasma, serum and purified vitellogenin. The results suggest that inhibition of lipoprotein lipase by vitellogenin requires the presence of charged phosphate groups on vitellogenin and an unoccupied heparin-binding site on the enzyme. Neither condition is likely to occur in the laying hen in vivo.
 ...
PMID:Does vitellogenin inhibit lipoprotein lipase in the laying hen? 309 31

Macrophages from both rodent and human sources have been shown to produce lipoprotein lipase (LPL), the enzyme activity of which can be measured in culture media and in cellular homogenates. The studies reported here show the presence of LPL on the surface of human monocyte-derived macrophages. An inhibitory monoclonal antibody to human LPL was used for cellular and immunoelectron microscopy studies. This antibody is a competitive inhibitor of LPL hydrolysis of triacylglycerol but does not inhibit LPL hydrolysis of a water-soluble substrate, p-nitrophenyl acetate. Furthermore, when postheparin plasma was mixed with monoclonal antibody prior to gel filtration on 6% agarose, the LPL activity eluted with the lipoproteins and was not inhibited by the antibody. These studies suggest that the antibody recognized the lipid/lipoprotein binding site of the LPL molecule. Membrane-bound LPL was demonstrated on human monocyte-derived macrophages using colloidal gold-protein A to detect the monoclonal antibody to LPL. The surface colloidal gold was randomly distributed with a surface density of 56,700 gold particles per cell. Control cells cultured in heparin-containing media (10 units/ml) or cells reacted with anti-hepatic triacylglycerol lipase monoclonal IgG or nonimmune mouse IgG did not exhibit membrane binding of protein A-gold. Macrophages were incubated with control and monoclonal anti-LPL IgGs and 125I-labeled anti-mouse IgG F(ab')2. Heparin-releasable membrane-bound anti-LPL antibody was demonstrated. These studies demonstrate the presence of LPL on the surface of human monocyte-derived macrophages, such that the LPL is oriented with its lipid-binding portion (recognized by this antibody) exposed. Membrane-associated LPL may be important in the interaction and subsequent uptake of lipid and lipoproteins by macrophages and in the generation of atherosclerotic foam cells.
 ...
PMID:Membrane-bound lipoprotein lipase on human monocyte-derived macrophages: localization by immunocolloidal gold technique. 335 47

Heparin can dissociate lipoprotein lipase from casein micelles, and addition of heparin enhances lipolysis in bovine but not in caprine milk. Heparin shortened the lag-time for binding of lipoprotein lipase to milk fat globules and for lipolysis. Heparin counteracted the inhibitory effects of skim milk on binding of lipase and on lipolysis. Heparin stimulated lipolysis in all bovine milk samples when added before cooling and in spontaneously lipolytic milk samples also when added after cooling. Heparin enhanced lipolysis of isolated milk fat globules. Hence, its effect is not solely due to dissociation of lipoprotein lipase from the casein micelles. Cooling of goat milk caused more marked changes in the distribution of lipase than cooling of bovine milk; the fraction of added 125I-labeled lipase that bound to cream increased from about 8 to 60%. In addition, caprine skim milk caused less inhibition of lipolysis than bovine skim milk. These observations provide an explanation for the high degree of cold storage lipolysis in goat milk. Heparin had only small effects on the distribution of lipoprotein lipase in caprine milk, which explains why heparin has so little effect on lipolysis in caprine milk. The distribution of 35S-labeled heparin in bovine milk was studied. In warm milk less than 10% bound to the cream fraction, but when milk was cooled, binding of heparin to cream increased to 45%.(ABSTRACT TRUNCATED AT 250 WORDS)
 ...
PMID:Hydrolysis of bovine and caprine milk fat globules by lipoprotein lipase. Effects of heparin and of skim milk on lipase distribution and on lipolysis. 344 3

The kinetics of inhibition of the esterase and lipase activities of bovine milk lipoprotein lipase (LPL) were compared. The esterase LPL activity against emulsified tributyrylglycerol was not affected by the enzyme activator apolipoprotein C-II (C-II) and amounted to about 15% of the "plus activator" lipase enzyme activity. Heparin at concentrations of 20 micrograms/ml inhibited 25% of the esterase activity. The reaction followed Henri-Michaelis-Menten kinetics and the inhibition by heparin followed a linear, intersecting, noncompetitive kinetic model. On the other hand, the basal lipase activity of LPL against emulsified trioleoylglycerol (TG) was very sensitive to inhibition by heparin: 1 microgram/ml inhibited about 80% of the reaction and 3 micrograms/ml drove the reaction to zero. The velocity curve for the uninhibited basal LPL activity was sigmoidal with an apparent nH(TG) of 2.94. Heparin inhibited the lipase activity competitively: heparin decreased nH(TG) and increased[TG]0.5 6.4-fold, while TG decreased the nH(Heparin) from 2.14 to 0.95 and caused a 3-fold increase in [Heparin]0.5. C-II, at concentrations lower than 2.5 X 10(-8) M (i.e., lower than KA), countered the inhibitory effects of heparin: at constant inhibitor concentrations, C-II increased nH(TG) from 1.78 to 2.52 and decreased [TG]0.5 about 10-fold; it also increased the apparent Vmax. At the lower C-II concentrations, nH(C-II) was approximately equal to 1.0 and increasing the TG concentrations decreased [C-II]0.5 from 3.8 X 10(-8) to 8.5 X 10(-9) M, with no effect on the nH(C-II). At the higher C-II concentrations, nH(C-II) was 2.5 and TG decreased [C-II]0.5 about 2-fold with no effect on the nH(C-II). In the absence of heparin, C-II had no effect on nH(TG) nor on [TG]0.5, but it increased the apparent Vmax. On the other hand, TG had no effect on nH(C-II) nor on [C-II]0.5, but at any given C-II concentration, the reaction velocity increased with increasing TG concentrations. It is concluded that TG and heparin as well as C-II and heparin are mutually exclusive and that lipoprotein lipase is a multisite enzyme, possibly a tetramer, with three high-affinity catalytic sites, and an equal number of sites for C-II and heparin per oligomer. However, LPL differs from classical allosteric enzymes in that its activator has no effect on substrate cooperativity nor on [S]0.5; its only effect is to increase Vmax by increasing the catalytic rate constant kp by inducing conformational changes in the enzyme.
 ...
PMID:The kinetics of heparin inhibition of the esterase and basal lipase activities of lipoprotein lipase. 356 88

Guinea-pig adipocytes released lipoprotein lipase activity to the medium without depletion of cell-associated lipoprotein lipase activity. Heparin caused immediate release of 20-25% of the lipase activity to the medium, and also enhanced the continued release. After addition of cycloheximide, cell-associated lipoprotein lipase activity decreased rapidly. Release of lipase activity to the medium continued unabated for about 30 min, but there was little release thereafter. The release accounted for only about 25% of the initial lipoprotein lipase activity in the absence and about 50% in the presence of heparin. In pulse-chase experiments with [35S]methionine, labeled lipoprotein lipase appeared in the medium within 40 min, and most of the release occurred during the first h of chase. In a 4-h chase the total (cells + medium) amount of labeled lipase decreased to 34%. Thus, degradation was a main fate of the lipase. Heparin markedly increased the amount of labeled lipase that was released to the medium and decreased the amount that was degraded. Heparin did not change the time-course for the release, and the amount of labeled lipase degraded was proportional to the amount not released to the medium, indicating that the effect of heparin was primarily on release, not on degradation as such. This study demonstrates that adipocytes synthesize lipoprotein lipase in excess of what is being released, and that the excess is rapidly degraded.
 ...
PMID:Mechanisms for turnover of lipoprotein lipase in guinea pig adipocytes. 362 Apr 83

Emulsions with lipid compositions similar to the triacylglycerol-rich lipoproteins were metabolized similarly to natural chylomicrons or very-low-density lipoproteins when injected intravenously in rats. Radioactive labels tracing the emulsion triacylglycerols and cholesteryl esters were both removed rapidly from the blood stream, but the removal rate of triacylglycerols was faster than that of cholesteryl ester. Most of the removed cholesteryl ester label was found in the liver, but only a small fraction of the triacylglycerol label was found in this organ, consistent with hepatic uptake of the remnants of the injected emulsion. Emulsions otherwise identical but excluding unesterified cholesterol were metabolized differently. The plasma removal of triacylglycerols remained fast, but the cholesteryl esters were removed very slowly. Heparin stimulated lipolysis, but failed to increase the rate of removal of cholesteryl esters from emulsions lacking cholesterol. Evidently, emulsions lacking cholesterol were acted on by the enzyme lipoprotein lipase, but the resultant triacylglycerol-depleted remnant particle remained in the plasma instead of being rapidly taken up by the liver. Therefore, the presence of emulsion cholesterol is a critical determinant of early metabolic events, and the findings point to a similar role for cholesterol in the natural triacylglycerol-rich lipoproteins.
 ...
PMID:Cholesterol is necessary for triacylglycerol-phospholipid emulsions to mimic the metabolism of lipoproteins. 362 Apr 86

The distribution of lipoprotein lipase among cream, casein, and milk serum can be evaluated by addition of a trace amount of 125I-labeled lipoprotein lipase to milk. Radioactive lipase was distributed in parallel to endogenous lipase under several conditions. In some milk samples, binding of lipase to cream increased when the milk was cooled. Correlation was good between bound labeled lipase and degree of cold-induced lipolysis in corresponding milk samples. Binding of lipase to cream or to casein was not saturable by addition of two-to threefold more lipase than is normally present in milk. In milk with a relatively high fraction of lipase bound to cream, a correspondingly lower fraction was associated with casein, whereas the fraction of lipase in milk serum was similar in all milk samples. Cold-induced binding of lipoprotein lipase to cream was not fully reversed when the milk was warmed again. Heparin released lipase from casein and increased the amount of lipase bound to cream after cooling.
 ...
PMID:Iodine-125-labeled lipoprotein lipase as a tool to detect and study spontaneous lipolysis in bovine milk. 374 79

Approximately 70% of the W/WV mice lacking mast cells due to a genetic defect showed hypertriglyceridemia combined with hypercholesterolemia. Increases of various magnitudes in chylomicrons, very-low-density lipoprotein, and intermediate-density lipoprotein were observed in the plasma of W/WV mice compared to those in the plasma of congenic normal mice. The increase in these lipoproteins was seen even in normolipidemic W/WV mice. Activities of both lipoprotein lipase and hepatic triacylglycerol lipase in the plasma after heparin injection were markedly lower in the W/WV mice than in the congenic normal mice, although activities of both lipoprotein lipase in the heart and adipose tissue and hepatic triacylglycerol lipase in the liver were not decreased. These results suggest that the W/WV mice have genetic defects in one or more of the following: secretion of both lipases from their synthesising cells, transport to the endothelium, and anchoring to the endothelial surface. Heparin deficiency in these mice may be responsible for the impairment and, thereby, may partially contribute to the hyperlipidemia.
 ...
PMID:Hyperlipidemia in mast cell-deficient W/WV mice. 375 4

Combined lipase deficiency (cld/cld) is a recessive mutation in mice which results in massive hyperlipemia and death within 3 days after birth. We studied the effect of this deficiency on lipolytic activities in liver and in pre- and postheparin plasma of mice less than 2 days old. Anti-hepatic lipase serum inhibited more than 85% of the lipolytic activity in liver and plasma of normal newborn mice when assayed in high-salt medium, validating the use of this medium for measuring hepatic lipase activity in mice. Anti-lipoprotein lipase serum, in contrast, inhibited only two-thirds of the lipolytic activity in liver and plasma when assayed in serum low-salt medium, and anti-hepatic lipase serum inhibited the rest. This indicates that assay with serum low-salt medium alone is not specific for lipoprotein lipase activity in mice. Therefore, immunoinhibition was used, as needed, for measuring lipoprotein lipase activity. The livers of unaffected newborn mice contained high levels of both hepatic and lipoprotein lipase activities, 228 and 187 mU/g, respectively. The plasma of unaffected mice contained a high level of hepatic lipase activity, 244 mU/ml, but practically no lipoprotein lipase activity. Heparin injected intraperitoneally increased plasma lipoprotein lipase activity to 152 mU/ml, but had no effect on plasma hepatic lipase activity, in unaffected mice. Hepatic lipase activity was virtually absent from both liver and plasma of cld/cld mice. Lipoprotein lipase activity was present in the liver at a surprisingly high level, 40% of that in normals, but was barely detectable in plasma. Heparin injection increased plasma lipoprotein lipase activity in cld/cld mice, but the increment was less than 10% of that in unaffected mice. Heparin had no significant effect on plasma hepatic lipase activity in defective mice. These findings confirm preliminary observations that hepatic lipase activity in liver and plasma and lipoprotein lipase activity in plasma are markedly reduced in combined lipase deficiency. The unexpected high level of lipoprotein lipase activity in liver of cld/cld mice suggests that regulation of lipoprotein lipase activity in liver of neonatal mice is different from that in other tissues.
 ...
PMID:Effect of combined lipase deficiency (cld/cld) on hepatic and lipoprotein lipase activities in liver and plasma of newborn mice. 395 63

Rats treated chronically with the anticancer agent adriamycin (1.5 mg/kg/week X 14 weeks) exhibited cardiac and renal lesions typical of anthracycline toxicity, and had serum hyperlipidemia characterized by 4 to 10 fold elevations in all lipoprotein classes. Heparin-releasable lipoprotein lipase activity measured in perfused heart preparations was decreased 69% in adriamycin-treated rats compared to saline-treated controls. Residual (non-heparin-releasable) activity was not significantly different after adriamycin treatment. The decrease in functional cardiac lipoprotein lipase may account, at least in part, for the serum hyperlipidemia observed in adriamycin-treated rats, and might play a role in the development of heart muscle disease.
 ...
PMID:Decreased cardiac lipoprotein lipase activity in rats treated chronically with adriamycin. 396 80


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>