Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “LIPASES”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources
PubMed1989

Structural features of lipoprotein lipase. Lipase family relationships, binding interactions, non-equivalence of lipase cofactors, vitellogenin similarities and functional subdivision of lipoprotein lipase.

A structural homology between lipoprotein lipase, pancreatic lipase and hepatic lipase is known and indicates that all three lipases are members of a common protein family. Lipoprotein lipase and pancreatic lipase utilize small protein co-factors, apolipoprotein C-II and co-lipase, respectively, but comparisons reveal no homology between the co-factor molecules. Hence, they do not show the same relationship as their target enzymes. Neither do screenings detect any extensive similarities between lipoprotein lipase, serine hydrolases, or apolipoproteins. Scannings against data bank proteins show that a 105-residue segment of lipoprotein lipases exhibits a 35-40% residue identity with a sub-region of Drosophila vitellogenins. One fifth of the conserved amino acid residues (8 of 40) are glycine, a pattern which is typical of distantly related forms of protein families. This supports a true relationship between large segments of Drosophila vitellogenins and lipases. Physiological and functional aspects of the vitellogenin/lipoprotein lipase similarities are given. The region concerned is entirely within the N-terminal domain of lipoprotein lipase and constitutes the segment where the similarity to hepatic and pancreatic lipases is most pronounced. Within this lipase region a 10-residue putative lipid-binding site exists for which further similarities have been found to the otherwise not closely related lingual/gastric lipases, prokaryotic lipases and lecithin-cholesterol acyltransferase. Another segment in lipoprotein lipase, where the heparin-binding site has been mapped, exhibits a correlation between strength of heparin binding and extent of basic residues among members of the lipase family. It further exhibits weak similarities with the 'Zn-finger' DNA-binding segment of steroid hormone receptors and may indicate convergence in a binding interaction. Thus, a functional subdivision of lipoprotein lipase into different segments can be distinguished.

Amino Acid Sequence↗
PubMed1999

Cloning and sequence analysis of the lipase and lipase chaperone-encoding genes from Acinetobacter calcoaceticus RAG-1, and redefinition of a proteobacterial lipase family and an analogous lipase chaperone family.

The genes encoding the lipase (LipA) and lipase chaperone (LipB) from Acinetobacter calcoaceticus RAG-1 were cloned and sequenced. The genes were isolated from a genomic DNA library by complementation of a lipase-deficient transposon mutant of the same strain. Transposon insertion in this mutant and three others was mapped to a single site in the chaperone gene. The deduced amino acid (aa) sequences for the lipase and its chaperone were found to encode mature proteins of 313 aa (32.5kDa) and 347 aa (38.6kDa), respectively. The lipase contained a putative leader sequence, as well as the conserved Ser, His, and Asp residues which are known to function as the catalytic triad in other lipases. A possible trans-membrane hydrophobic helix was identified in the N-terminal region of the chaperone. Phylogenetic comparisons showed that LipA, together with the lipases of A. calcoaceticus BD413, Vibrio cholerae El Tor, and Proteus vulgaris K80, were members of a previously described family of Pseudomonas and Burkholderia lipases. This new family, which we redefine as the Group I Proteobacterial lipases, was subdivided into four subfamilies on the basis of overall sequence homology and conservation of residues which are unique to the subfamilies. LipB, moreover, was found to be a member of an analogous family of lipase chaperones. We propose that the lipases produced by P. fluorescens and Serratia marcescens, which comprise a second sequence family, be referred to as the Group II Proteobacterial lipases. Evidence is provided to support the hypothesis that both the Group I and Group II families have evolved from a combination of common descent and lateral gene transfer.

Acinetobacter calcoaceticus↗
PubMed1996

Hormone-sensitive lipase is structurally related to acetylcholinesterase, bile salt-stimulated lipase, and several fungal lipases. Building of a three-dimensional model for the catalytic domain of hormone-sensitive lipase.

Hormone-sensitive lipase is the key enzyme in the mobilization of fatty acids from adipose tissue, thereby playing a crucial role in the overall energy homeostasis in mammals. Its activity is stimulated by catecholamines through cAMP-dependent phosphorylation of a single serine, a process that is prevented by insulin. This regulatory property is unique to this enzyme among all known lipases and has been acquired during evolution through insertion of a regulatory module into an ancestral lipase. Sequence alignments have failed to detect significant homology between hormone-sensitive lipase and the rest of the mammalian lipases and esterases, to which this enzyme is only very distantly related. In the present work, we report the finding of a remarkable secondary structure homology between hormone-sensitive lipase and the enzymes from a superfamily of esterases and lipases that includes acetylcholinesterase, bile salt-stimulated lipase, and several fungal lipases. This finding, based on the identification of the secondary structure elements in the hormone-sensitive lipase sequence, has allowed us to construct a three-dimensional model for the catalytic domain of hormone-sensitive lipase. The model reveals the topological organization, predicts the components of the catalytic triad, suggests a three-dimensional localization of the regulatory module, and provides a valuable tool for the future study of structural and functional aspects of this metabolically important enzyme.

Acetylcholinesterase↗
PubMed1993

Chromosomal localization of lipolytic enzymes in the mouse: pancreatic lipase, colipase, hormone-sensitive lipase, hepatic lipase, and carboxyl ester lipase.

Several lipases and their cofactors are involved in the absorption, transport, storage, and mobilization of lipids. As part of an effort to examine the role of these enzymes in plasma lipid metabolism and genetic susceptibility to atherosclerosis, we report the chromosomal mapping of their genes in mouse. Restriction fragment length variants for each gene were identified, typed in an interspecific cross, and tested for linkage to known chromosomal markers. The gene for pancreatic lipase resides on chromosome 19, while the gene for its cofactor, colipase, is on chromosome 17. A gene for a protein with sequence similarity to pancreatic lipase was tightly linked (no observed recombination) to the gene for pancreatic lipase, suggesting a gene cluster. The gene for hormone-sensitive lipase is near the gene cluster containing apolipoproteins C-II and E on chromosome 7. The gene for hepatic lipase is near the gene for apolipoprotein A-I on chromosome 9. The carboxyl ester lipase gene resides on chromosome 2. Previously, we have mapped the gene for lipoprotein lipase to chromosome 8. Thus, with the exception of pancreatic lipase and a related protein, these lipase genes, including several that are members of a gene family, are widely dispersed in the genome. Comparison of chromosomal locations for these genes in mouse and humans shows that the previously observed interspecies syntenies are preserved.

Animals↗
PubMed1998

Combined lipase deficiency (cld/cld) in mice affects differently post-translational processing of lipoprotein lipase, hepatic lipase and pancreatic lipase.

Lipoprotein lipase (LPL) and hepatic lipase (HL), which act on plasma lipoproteins, belong to the same gene family as pancreatic lipase. LPL is synthesized in heart, muscle and adipose tissue, while HL is synthesized primarily in liver. LPL is also synthesized in liver of newborn rodents. The active form of LPL is a dimer, whereas that of HL has not been established. Combined lipase deficiency (CLD) is an autosomal recessive mutation (cld) in mice which impairs post-translational processing of LPL and HL. Cld/cld mice have very low LPL and HL activities (< 5% of normal), yet normal pancreatic lipase activity. They develop massive hypertriglyceridemia and die within 3 days after birth. The CLD mutation allows synthesis, glycosylation and dimerization of LPL, but blocks activation and secretion of the lipase. Thus, dimerization per se does not result in production of active LPL. Immunofluorescence studies showed that LPL is retained in endoplasmic reticulum (ER) in cld/cld cells. Translocation of Golgi components to ER by treatment with brefeldin A (BFA) enabled synthesis of active LPL in cultured cld/cld brown adipocytes. Thus, production of inactive LPL in cld/cld cells results from inability of the cells to transport LPL from ER. The CLD mutation allows synthesis and glycosylation of HL, but blocks activation of the lipase. Immunofluorescence studies located HL mostly outside of cells in liver, liver cell cultures and incubated adrenal tissue of normal and cld/cld mice and mostly inside of cells in liver cell cultures and adrenal tissues treated with monensin (to block secretion of protein). These findings demonstrate synthesis and secretion of HL by both liver and adrenal cells of normal and cld/cld mice. Thus, the CLD mutation allows secretion of inactive HL by liver and adrenals. However, it does not block synthesis or secretion of active pancreatic lipase. Our findings indicate that LPL, HL and pancreatic lipase, although closely related, are processed differently.

Animals↗
PubMed2004

Use of immobilized lipases for lipase purification via specific lipase-lipase interactions.

Lipase from Pseudomonas fluorescens (PFL), an enzyme with a great tendency to yield bimolecular aggregates, was immobilized via multipoint covalent attachment on glyoxyl-agarose in the presence of Triton X-100. This strategy permitted to obtain the enzyme with the active center oriented towards the reaction medium. This immobilized enzyme presents the capacity of specifically adsorbing PFL molecules, that can be easily desorbed by the use of detergents. More interesting, the enzyme was also able to adsorb other lipases. That is, the lipase from Bacillus thermocatenulatus (BTL2) cloned in Escherichia coli was selectively adsorbed on this immobilized enzyme, enabling a very simple purification strategy. Similar results were achieved with some other lipases (those from Rhizomucor miehei (RML), Rhizopus oryzae (ROL), and Humicola Lanuginosa (HLL)). In all cases, the enzyme could be easily desorbed by incubation with Triton X-100. The matrix could be used several cycles without any detrimental effect on the adsorption capacity.

Electrophoresis, Polyacrylamide Gel↗
PubMed1988

Lingual and gastric lipases: species differences in the origin of prepancreatic digestive lipases and in the localization of gastric lipase.

The source of the lipase(s) acting in the stomach was investigated in five animal species: rat, mouse (rodents), rabbit (lagomorphs), guinea pig (caviidae), baboon and human (primates). The activity of lingual and gastric lipases was quantitated in homogenates of lingual serous glands and of gastric mucosa, respectively, by the hydrolysis of tri[3H]oleylglycerol and is expressed in units/g (1 U = 1 mumol [3H]oleic acid released/min) per g tissue wet weight, mean +/- S.E. There were marked differences in the activity level of lingual and gastric lipases among species: mouse and rat had high levels of lingual lipase activity (250 +/- 20 and 824 +/- 224 U/g) and only traces of gastric lipase activity (4.5 +/- 0.9 and 0.04 U/g, respectively), whereas rabbit and guinea pig had no lingual lipase activity and only gastric lipase activity (78 +/- 48 and 27 +/- 7.4 U/g, respectively). In the baboon and human, gastric lipase was the predominant enzyme (109 +/- 20 U/g and 118 +/- 8.8 U/g, respectively), whereas lingual lipase activity was present in trace amounts only (0.04 U/g and 0.3 U/g, respectively). In addition to species differences in the origin of the preduodenal lipases, there were also species differences in the distribution of gastric lipase in the stomach. Thus, while in the rabbit, gastric lipase was localized exclusively in the cardia and body of the stomach, it was diffusely distributed in the entire stomach of the guinea pig and baboon. A comparison between the level of activity of lipase and pepsin (the two chief digestive enzymes secreted by the stomach), showed differences in their localization in the species studied. The difference in source (tongue vs. stomach) and site (cardia-body vs. entire stomach) of lipase secretion must be taken into account in future studies of these digestive enzymes. Although the exact contribution of lingual and gastric lipases individually to fat digestion in species which contain both enzymes cannot yet be evaluated, the markedly higher levels of gastric lipase activity in the baboon and human suggests that, in primates, gastric lipase is probably the major non-pancreatic digestive lipase.

Animals↗
PubMed1995

Lipase evolution: trout, Xenopus and chicken have lipoprotein lipase and apolipoprotein C-II-like activity but lack hepatic lipase-like activity.

Lipoprotein lipase and hepatic lipase are members of a gene family which also contains pancreatic lipase. High activity of lipoprotein lipase is present in extrahepatic tissues in all mammals studied and also in birds. The activity of hepatic lipase varies more. To investigate the evolutionary relationship, lipase activities in tissues of some lower vertebrates were measured. In fish and in frog, low activities with the characteristics of lipoprotein lipase were found. Serum from frog and from fish, and plasma from chicken, stimulated lipoprotein lipase in vitro, indicating that these species contain analogues to human apolipoprotein C-II. Little or no hepatic lipase-like activity was found in post-heparin plasma or in liver homogenates of chickens. In fish liver, lipase activity with an apparent heparin affinity similar to, or even higher than lipoprotein lipase was found. Frog liver contained a small amount of lipase activity with high heparin affinity. This activity was inhibited both by apolipoprotein C-II and by 1 M NaCl. It is not clear whether the low lipase activities in livers from fish and from frog are variants of hepatic lipase. Since lipoprotein lipase and apolipoprotein C-II are already present in fish, this lipase probably evolved before hepatic lipase.

Animals↗
PubMed1988

Human hepatic lipase. Cloned cDNA sequence, restriction fragment length polymorphisms, chromosomal localization, and evolutionary relationships with lipoprotein lipase and pancreatic lipase.

Human hepatic lipase is an important enzyme in high density lipoprotein (HDL) metabolism, being implicated in the conversion of HDL2 to HDL3. Three human hepatic lipase cDNA clones were identified in two lambda gt11 libraries from human liver. The cDNA-derived amino acid sequence predicts a protein of 476 amino acid residues, preceded by a 23-residue signal peptide. Four potential N-glycosylation sites are identified, two of which are conserved in rat hepatic lipase. On alignment with human, mouse, and bovine lipoprotein lipase, the same two sites were also conserved in lipoprotein lipase in all three species. Stringent conservation of the cysteine residues was also evident. Comparative analysis of amino acid sequences shows that hepatic lipase evolves at a rapid rate, 2.07 x 10(-9) substitutions/site/year, about four times that in lipoprotein lipase and half that in pancreatic lipase. Further, hepatic lipase and pancreatic lipase appear to be evolutionarily closer to each other than either of them is to lipoprotein lipase. Southern blot analysis revealed high frequency restriction fragment length polymorphisms of the hepatic lipase gene for the enzymes HindIII and MspI. these polymorphisms will be useful for haplotype and linkage analysis of the hepatic lipase gene. Using cloned human hepatic lipase cDNA as a hybridization probe, we performed Southern blot analysis of a panel of 13 human-rodent somatic cell hybrids. Concordance analysis of the various hybrid clones indicates that the hepatic lipase gene is located on the long arm of human chromosome 15. Analysis of hybrids containing different translocations of chromosome 15 localized the gene to the region 15q15----q22.

Amino Acids↗
PubMed1990

The complete digestion of human milk triacylglycerol in vitro requires gastric lipase, pancreatic colipase-dependent lipase, and bile salt-stimulated lipase.

Gastric lipase, pancreatic colipase-dependent lipase, and bile salt-stimulated lipase all have potential roles in digestion of human milk triacylglycerol. To reveal the function of each lipase, an in vitro study was carried out with purified lipases and cofactors, and with human milk as substrate. Conditions were chosen to resemble those of the physiologic environment in the gastrointestinal tract of breast-fed infants. Gastric lipase was unique in its ability to initiate hydrolysis of milk triacylglycerol. Activated bile salt-stimulated lipase could not on its own hydrolyze native milk fat globule triacylglycerol, whereas a limited hydrolysis by gastric lipase triggered hydrolysis by bile salt-stimulated lipase. Gastric lipase and colipase-dependent lipase, in combination, hydrolyzed about two thirds of total ester bonds, with monoacylglycerol and fatty acids being the end products. Addition of bile salt-stimulated lipase resulted in hydrolysis also of monoacylglycerol. When acting together with colipase-dependent lipase, bile salt-stimulated lipase contributed also to digestion of tri- and diacylglycerol. We conclude that digestion of human milk triacylglycerol depends on three lipases with unique, only partly overlapping, functions. Their concerted action results in complete digestion with free glycerol and fatty acids as final products.

Bile Acids and Salts↗
PubMed1985

Purification and characterization of human lipoprotein lipase and hepatic triglyceride lipase. Reactivity with monoclonal antibodies to hepatic triglyceride lipase.

Human lipoprotein lipase and hepatic triglyceride lipase were purified to homogeneity from post-heparin plasma. These enzymes were purified 250,000- and 100,000-fold with yields of 27 +/- 15 and 19 +/- 6%, respectively. Molecular weight determination by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate and reducing agents yielded Mr of 60,500 +/- 1,800 and 65,200 +/- 400, respectively, for lipoprotein lipase and hepatic triglyceride lipase. These lipase preparations were shown to be free of detectable antithrombin by measuring its activity and by probing of Western blots of lipases with a monospecific antibody against antithrombin. In additions, probing of Western blots with concanavalin A revealed no glycoproteins corresponding to the molecular weight of antithrombin. Four stable hybridoma-producing distinct monoclonal antibodies (mAb) to hepatic triglyceride lipase were isolated. The specificity of one mAb, HL3-5, was established by its ability to immunoprecipitate hepatic triglyceride lipase catalytic activity. Interaction of HL3-5 with this lipase did not inhibit catalytic activity. The three other mAb interacted with hepatic triglyceride lipase only after denaturation of the enzyme with detergents. The relatedness of these two enzymes was examined by comparing under the same conditions the thermal inactivation, the sensitivity to sulfhydryl and reducing agents, amino acid composition, and the mobility of peptide fragments generated by cyanogen bromide cleavage. The results of these studies strongly support the view that the two enzymes are different proteins. Immunological studies confirm this conclusion. Four mAb to hepatic triglyceride lipase did not interact with lipoprotein lipase in Western blots, enzyme-linked immunosorbent assay, and immunoprecipitation experiments. These immunological studies demonstrate that several epitopes of the hepatic triglyceride lipase protein moiety are not present in the lipoprotein lipase molecule.

Amino Acids↗
PubMed1991

Domain exchange: characterization of a chimeric lipase of hepatic lipase and lipoprotein lipase.

Hepatic lipase and lipoprotein lipase hydrolyze fatty acids from triacylglycerols and are critical in the metabolism of circulating lipoproteins. The two lipases are similar in size and amino acid sequence but are distinguished by functional differences in substrate preference and cofactor requirement. Presumably, these distinctions result from structural differences in functional domains. To begin localization of these domains, a chimeric lipase was constructed composed of the N-terminal 329 residues of rat hepatic lipase linked to the C-terminal 136 residues of human lipoprotein lipase. The chimera hydrolyzed both monodisperse short-chain (esterase) and emulsified long-chain (lipase) triacylglycerol substrates with catalytic and kinetic properties closely resembling those of native hepatic lipase. However, monoclonal antibodies to lipoprotein lipase inhibited the lipase activity, but not the esterase function, of the chimera. Therefore, the chimeric molecule is a functional lipase and contains elements and characteristics from both parental enzymes. It is proposed that the N-terminal domain, containing the active center from hepatic lipase, governs the catalytic character of the chimera, and the C-terminal domain is essential for hydrolysis of long-chain substrates.

Amino Acid Sequence↗
PubMed1982

Triacylglycerol lipase, monoacylglycerol lipase and phospholipase activities of highly purified rat hepatic lipase.

Highly purified rat hepatic lipase (NaCl-resistant, alkaline pH optimum) was studied to evaluate whether the enzyme has triacylglycerol lipase, monoacylglycerol lipase and phospholipase activities. Enzyme exhibiting a single band by SDS-polyacrylamide gel electrophoresis and having a specific activity eight times greater than that in any previous report was utilized. The ratios of the different lipolytic activities to each other remained constant throughout a multistep hepatic lipase purification. The lipolytic activities coeluted by gel filtration on Ultrogel AcA 34. Column isoelectric focusing of the highly purified enzyme revealed comigration of the lipolytic activities. Thermal inactivation produced similar decay curves for the different activities. Immune titration curves for the different activities with specific antibody against hepatic lipase were essentially identical. These findings indicate that hepatic lipase is a single enzyme molecule which has triacyglycerol lipase, monoacylglycerol lipase and phospholipase activities with artificial substrates. To study these lipolytic activities further, purified hepatic lipase was subjected to limited digestion by specific proteases. The triacylglycerol lipase activity was more sensitive to proteolytic destruction than either of the other two activities.

Animals↗
PubMed1995

Characterization of lipase-deficient mutants of Acinetobacter calcoaceticus BD413: identification of a periplasmic lipase chaperone essential for the production of extracellular lipase.

Acinetobacter calcoaceticus BD413 produces an extracellular lipase, which is encoded by the lipA gene. Five lipase-deficient mutants have been generated via random insertion mutagenesis. Phenotypic characterization of these mutants revealed the presence of as many as four lipolytic enzymes in A. calcoaceticus. Biochemical evidence classified four of the mutants as export mutants, which presumably are defective in translocation of the lipase across the outer membrane. The additional mutant, designated AAC302, displays a LipA- phenotype, and yet the mutation in this strain was localized 0.84 kbp upstream of lipA. Sequence analysis of this region revealed an open reading frame, designated lipB, that is disrupted in AAC302. The protein encoded by this open reading frame shows extensive similarity to a chaperone-like helper protein of several pseudomonads, required for the production of extracellular lipase. Via complementation of AAC302 with a functional extrachromosomal copy of lipA, it could be determined that LipB is essential for lipase production. As shown by the use of a translational LipB-PhoA fusion construct, the C-terminal part of LipB of A. calcoaceticus BD413 is located outside the cytoplasm. Sequence analysis further strongly suggests that A. calcoaceticus LipB is N terminally anchored in the cytoplasmic membrane. Therefore, analogous to the situation in Pseudomonas species, however, lipB in A. calcoaceticus is located upstream of the structural lipase gene. lipB and lipA form a bicistronic operon, and the two genes are cotranscribed from an Escherichia coli sigma 70-type promoter. The reversed order of genes, in comparison with the situation in Pseudomonas species, suggests that LipA and LipB are produced in equimolar amounts. Therefore, the helper protein presumably does not only have a catalytic function, e.g., in folding of the lipase, but is also likely to act as a lipase-specific chaperone. A detailed model of the export route of the lipase of A. calcoaceticus BD413 is proposed.

Acinetobacter calcoaceticus↗
PubMed1993

Functional characterization of a chimeric lipase genetically engineered from human lipoprotein lipase and human hepatic lipase.

Lipoprotein lipase (LPL) and hepatic lipase (HL) mediate the hydrolysis of triglycerides and phospholipids present in circulating lipoprotein particles and are essential for normal lipid metabolism. Both enzymes have a similar primary amino acid structure and share requirements for intact catalytic, lipid binding, and heparin binding domains. However, LPL and HL exhibit different substrate specificities and cofactor requirements. In order to characterize the functional domains necessary for LPL activity, a chimeric lipase consisting of the amino-terminal 314 amino acids of human LPL and the carboxyl-terminal 146 amino acids of human HL was synthesized by joining the cDNA of both lipases at the 5'-end of exon 7. Northern blot hybridization and Western blot analyses revealed the size of the chimera mRNA and protein to be approximately 1.5 kb and 55 kDa, respectively. The chimeric enzyme hydrolyzed both long chain and short chain fatty acid triacylglycerols and had catalytic properties that were similar to lipoprotein lipase. Thus, apolipoprotein (apo)C-II was required for maximal lipase activity, and high salt concentration abolished the ability of the chimera to hydrolyze triolein even in the presence of apoC-II. A monospecific anti-HL polyclonal antibody interacting with the C-terminal HL-derived domain of the chimeric enzyme abolished the enzyme's ability to hydrolyze triglyceride emulsion but not tributyrin substrates. Analysis of the heparin binding properties of the chimeric enzyme using heparin-Sepharose affinity chromatography revealed an elution pattern which was intermediate between that of lipoprotein and hepatic lipase. In summary, we have characterized the functional properties of an LPL-HL chimeric enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗
PubMed1982

Fate of milk 125I-labelled lipoprotein lipase in cells in culture. Comparison of lipoprotein lipase- and non-lipoprotein lipase-synthesizing cells.

Radioiodinated lipoprotein lipase, isolated from bovine milk (125I-labeled milk lipoprotein lipase) was shown to retain full hydrolytic activity towards its native substrate, i.e., chylomicron triacylglycerol. The 125I-labeled enzyme interacted with various cells in culture by being bound to the cellular surface, internalized and degraded. Cellular binding of the labeled enzyme occurred in the presence or absence of substrate and was related to enzyme concentration. Heparin reduced cellular binding by 50% but inhibited uptake and degradation more extensively. Cellular uptake was not affected by chloroquine or NH4Cl, but degradation of the labeled enzyme was blocked. Uptake and degradation were not inhibited by mannose 6-phosphate. The interaction between the exogenous enzyme and cells which do not synthesize lipoprotein lipase, i.e., fibroblasts and endothelial cells, resulted in a high ratio of surface binding to degradation. In heart cell cultures and preadipocyte cultures, which produce lipoprotein lipase, the ratio of enzyme catabolized to that bound was high at all time points examined. Since in the intact organism lipoprotein lipase acts at the luminal surface of vascular endothelium, it seems expedient that these cells are able to bind the enzyme, but will catabolize it only slowly. The rapid and extensive degradation of the 125I-labeled lipoprotein lipase in heart cells and preadipocytes may be related to the metabolism of the endogenously produced lipoprotein lipase.

Adipose Tissue↗
PubMed1977

Selective protamine sulphate inactivation of lipoprotein lipase and hepatic lipase in human post-heparin plasma: specific lipase levels in normals and in type I hyperlipoproteinaemia.

The rate of inactivation of triglyceride hydrolase activity by protamine sulphate was determined in pooled, normal, post-heparin plasma. Two distinct first-order rates of inactivation were obtained and the derived constants used to calculate the lipoprotein lipase and hepatic lipase contributions to the total post-heparin triglyceride hydrolase activity in normal controls and in patients with familial hyperchylomicronaemia. The lipoprotein lipase was reduced in the patients whereas the hepatic lipase was normal. There was however a marked age-related increase in the hepatic enzyme activity in normal subjects. Post-heparin lipolytic activity, assayed in vitro against lipoproteins of d less than 1.006 derived from the patients, was markedly reduced in our hyperchylomicronaemic subjects. This assay correlated well with the lipoprotein lipase activity determined by selective protamine sulphate inactivation.

Adolescent↗