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T Olivecrona

Publications and source records attributed to T Olivecrona.

At least 145 records · Page 8Linked to original sources
PubMed1981

Lipoprotein lipase: modification of its kinetic properties by mild tryptic digestion.

Mild tryptic digestion of lipoprotein lipase cleaved its polypeptide chain in the middle, but the pieces were held together by disulphide bonds. The modified enzyme retained its ability to bind to heparin and to anionic detergents and on gel filtration it eluted in a similar position as the native enzyme does. It also retained essentially full activity against soluble substrates. Thus, the overall physico-chemical properties of the enzyme were not markedly changed and its active site remained intact after treatment with trypsin. The activity of the modified enzyme against long-chain acylglycerols and phospholipids was, however, much reduced. With some emulsions, the decreased activity could be ascribed in part to a decreased ability of the modified enzyme to bind to the emulsion droplets. Under these conditions apolipoprotein CII partially restored both binding and activity. With a lysophosphatidylcholine-triacylglycerol emulsion the modified enzyme adsorbed almost completely to the emulsion droplets, but its activity was nonetheless very low. Thus, tryptic cleavage interfered with the ability of the enzyme to become properly orientated at the interface. With this emulsion apolipoprotein CII enhanced the activity of the native enzyme fourfold but the activity of the trypsin-treated enzyme 30-fold, so that the activity of the modified enzyme became almost as high as that of the native enzyme. It is concluded that apolipoprotein CII enhances the activity of lipoprotein lipase by stabilizing an effective orientation/conformation of the enzyme at the interface. This effect became more marked when the ability of the enzyme itself to attain this form had been reduced by tryptic cleavage.

Animals↗
PubMed1981

Hydrolysis of human milk fat globules by pancreatic lipase: role of colipase, phospholipase A2, and bile salts.

Human milk fat globules were used to explore how dietary triglycerides are hydrolyzed by pancreatic lipase. These triglycerides were hydrolyzed very slowly by lipase alone as if the surface layer of proteins and phospholipids impeded the action of the enzyme. The inhibition of lipase activity could be overcome by addition either of colipase or of pancreatic phospholipase A2. Colipase enhanced triglyceride hydrolysis in a dose-dependent manner whether bile salts were present or not. Bile salts had no effect on the activity of pancreatic lipase alone but further enhanced the activity at all concentrations of colipase tested. Bile salts were a prerequisite to relieve inhibition of lipase activity by phospholipase A2. Human milk fat globules exposed to phospholipase A2 should be representative of a physiological substrate for pancreatic lipase. A major new observation was that bile salts, even at high concentrations, stimulated triglyceride hydrolysis of such phospholipase-treated globules by pancreatic lipase also in the absence of colipase.

Bile Acids and Salts↗
PubMed1980

Interaction of lipoprotein lipase with native and modified heparin-like polysaccharides.

1. Lipoprotein lipase (EC 3.1.1.34), which was previously shown to bind to immobilized heparin, was now found to bind also to heparan sulphate and dermatan sulphate and to some extent to chondroitin sulphate. 2. The relative binding affinities were compared by determining (a) the concentration of NaCl required to release the enzyme from polysaccharide-substituted Sepharose; (b) the concentration of free polysaccharides required to displace the enzyme from immobilized polysaccharides; and (c) the total amounts of enzyme bound after saturation of immobilized polysaccharides. By each of these criteria heparin bound the enzyme most efficiently, followed by heparan sulphate and dermatan sulphate, which were more efficient than chondroitin sulphate. 3. Heparin fractions with high and low affinity for antithrombin, respectively, did not differ with regard to affinity for lipoprotein lipase. 4. Partially N-desulphated heparin (40-50% of N-unsubstituted glucosamine residues) was unable to displace lipoprotein lipase from immobilized heparin. This ability was restored by re-N-sulphation or by N-acetylation; the N-acetylated product was essentially devoid of anticoagulant activity. 5. Partial depolymerization of heparin led to a decrease in ability to displace lipoprotein lipase from heparin-Sepharose; however, even fragments of less than decasaccharide size showed definite enzyme-releasing activity. 6. Studies with hepatic lipase (purified from rat post-heparin plasma) gave results similar to those obtained with milk lipoprotein lipase. However, the interaction between the hepatic lipase and the glycosaminoglycans was weaker and was abolished at lower concentrations of NaCl. 7. The ability of the polysaccharides to release lipoprotein lipase to the circulating blood after intravenous injection into rats essentially conformed to their affinity for the enzyme as evaluated by the experiments in vitro.

Animals↗
PubMed1980

Lipoprotein lipase: some effects of activator proteins.

This paper considers how apolipoprotein CII from human plasma lipoproteins and T1 and T2 proteins from egg yolk lipoproteins stimulate the activity of lipoprotein lipase. These activator proteins stabilized the enzyme much more effectively than a thousandfold higher concentration of albumin did, indicating a direct interaction with the enzyme. The effects of the activators were seen also at 1 M NaCl. Thus, forces other than electrostatic are implicated. Centrifugation experiments showed that 125I-labeled lipase bound equally well to the emulsion droplets in the absence of activator protein as in its presence. This was true even under conditions when the activator caused a severalfold increase in the rate of hydrolysis. Thus, the activator makes enzyme at the interface more effective in hydrolysis. By optimizing the conditions it was possible to obtain almost as high rates of triglyceride hydrolysis in the absence as in the presence of activator. Thus, the main effect of the activator protein is probably not on a rate-limiting chemical step. Under most conditions, the rate of hydrolysis was much below optimal and activator increased it. This was always the case with phosphatidyl-choline/triglyceride emulsions, where the activator enhanced hydrolysis of both lipids. Other experiments showed that the activator enhanced triglyceride hydrolysis in the absence of phospholipids and phospholipid hydrolysis in the absence of triglycerides. It is suggested that interaction with activator orientates the enzyme and/or the lipid substrate for effective hydrolysis at the surface of lipoproteins/model substrates.

Animals↗
PubMed1980

Lipoprotein lipase. Mechanism of product inhibition.

The rate at which lipoprotein lipase hydrolyzes triglycerides in lipoproteins and in synthetic emulsions decreases sharply with the amount of products formed unless albumin is present. Three factors which contribute to this inhibition as follows. (a) The fatty acids and the monoglycerides formed on hydrolysis locate at the lipid-water interface of the emulsion and, since they are substrates for the enzyme, act as competitive inhibitors of triglyceride hydrolysis. (b) The enzyme forms complexes with fatty acids. Therefore, as fatty acids accumulate in the system some of the enzyme will be sequestered into enzyme-fatty acid complexes. Albumin can prevent formation of such complexes since it has a higher affinity for fatty acids than the enzyme has. (c) Activator proteins do not enhance triglyceride hydrolysis unless a fatty acid acceptor is present. The strong inhibition of the enzyme itself and the loss of lipolysis-stimulating effects of activator proteins provide a feed-back regulation of the action of the lipase on lipoproteins at the capillary endothelium, ensuring that products are not generated more rapidly than they are utilized by the tissue.

Albumins↗
PubMed1980

The role of different albumin preparations on production of human plasma lipoprotein-like particles in vitro.

Because we found apoprotein contamination of some high-grade commercial albumins, we studied this effect on formation of lipoprotein-like particles during lipolysis of human very low density lipoprotein (VLDL) in vitro. After a 1-hr incubation with purified bovine milk lipoprotein lipase, over 98% VLDL triglyceride was hydrolyzed in the presence of either albumin B (apoprotein-rich) or albumin C (apoprotein-poor), with a weight ratio of albumin to triglyceride of 60 to 1. Lipoproteins of density < 1.019 g/ml ("IDL"), 1.019 to 1.063 g/ml ("LDL"), and 1.063 to 1.21 g/ml ("HDL") were then isolated by ultracentrifugation. Recovery of non-triglyceride VLDL constituents in "IDL" and "LDL" was similar for albumin B or albumin C. "LDL" was the major catabolic product of in vitro VLDL lipolysis independent of the albumin used. The yield of "HDL," however, was 5- to 6-fold greater with albumin B. All lipoproteins produced with albumin B were richer in phospholipid, apoproteins C and A-I, relative to lipoproteins produced in the presence of albumin C. With albumin B, cholesterol/phospholipid molar ratios were <1 in all in vitro produced lipoproteins, but were >1 with albumin C. All these differences can be ascribed to the presence in albumin B of 0.2 mg apoprotein A-I/g albumin and 1.8 mg phospholipid/g albumin; these components were not detected in albumin C. Thus, two thirds of "HDL" recovered with VLDL lipolysis in the presence of albumin B can be accounted for by albumin itself and only one third from constituents of VLDL. Adding equivalent amounts of both apoproteins removed from albumin B and phospholipid to albumin C markedly decreased the disparities in results but addition of each alone did not. These results prove "inert" albumins serve other than as fatty acid and lysolecithin acceptors in in vitro model systems, and do influence formation of lipoproteins during in vitro VLDL catabolism.-Deckelbaum, R. J., T. Olivecrona, and M. Fainaru. The role of different albumin preparations on production of human plasma lipoprotein-like particles in vitro.

Albumins↗
PubMed1979

Very low density lipoprotein. Removal of Apolipoproteins C-II and C-III-1 during lipolysis in vitro.

In this study we have investigated the effects of very low density lipoprotein (VLDL) lipolysis on the removal of radiolabeled apolipoprotein C-II and apolipoprotein C-III-1 from in vitro lipolyzed lipoproteins. Lipolysis was carried out in vitro using lipoprotein lipase purified from bovine milk, and mixtures with or without plasma. Lipoproteins were isolated by ultracentrifugation and by gel filtration. Labeled apo-C-II and apo-C-III-1 distributed among plasma lipoproteins, predominantly VLDL and high density lipoprotein (HDL). Lipolysis induced transfer of apo-C-II and apo-C-III-1 from VLDL to HDL. The transfer was proportional to the extent of triglyceride hydrolysis, and similar for the two apoproteins. The apo-C-II/apo-C-III-1 radioactivity ratio did not change in either VLDL or the fraction of d greater than 1.006 g/ml during the progression of the lipolytic process. Similar observations were recorded while using plasma-devoid lipolytic systems. Gel filtration of incubation mixtures, on 6% agarose, revealed that the removal of labeled apo-C molecules from VLDL is not a consequence of either centrifugation or high salt concentration. These results suggest that there is no preferential removal of apo-C-II or apo-C-III-1 from lipolyzed VLDL particles. They further indicate that the ratio of apo-C-II to apo-C-III-1 does not regulate the extent of lipolysis of different VLDL particles, at least in VLDL isolated from normolipidemic humans.

Animals↗
PubMed1979

Guinea pig very low density lipoproteins are a good substrate for lipoprotein lipase.

In contrast to plasma from most other animals, guinea pig plasma causes little or no stimulation of lipoprotein lipase activity. Very low density lipoproteins (VLDL) isolated by ultracentrifugation of guinea pig serum caused a definite stimulation of lipase activity, whereas the infranatant inhibited the activity. Gel filtration in 5 M guanidinium hydrochloride of delipidated VLDL demonstrated that the activation was caused by a low molecular weight protein. The VLDL themselves were hydrolized at similar rates as human VLDL both by guinea pig and by bovine lipoprotein lipases. Thus, guinea pig VLDL contain an activator for lipoprotein lipase analogous to that in other animals and there is enough of the activator to support rapid hydrolysis of the VLDL lipids by the lipase.

Animals↗
PubMed1979

Rapid removal to the liver of intravenously injected lipoprotein lipase.

Lipoprotein lipase was purified from bovine milk and labeled with 125I. After intravenous injection to rats the labeled lipase rapidly disappeared from the blood. The initial half-life was about 1 min and more than 70% of the radioactivity was found in the liver at 10 min. 30 min after the injection about 10% of the injected radioactivity was present in acid-soluble form in blood, indicating that the enzyme had been rapidly degraded. Injection of asialofetuin, ribonuclease B or mannan in amounts known to block the hepatic receptors for glycoproteins with exposed galactose, N-acetylglucosamine or mannose residues did not retard the removal of the lipoprotein lipase. Thus, some other, as yet undefined, receptor is implicated. Lipoprotein lipase is known to bind to heparin and some related polysacchrides. Heparin injected before the enzyme delayed its removal and heparin injected after the enzyme caused an immediate increase in blood radioactivity, signifying return from tissues to blood of labeled enzyme. Lipoprotein lipase is present at the endothelium in several extrahepatic tissues and is rapidly turned over. Its presence in blood in appreciable amounts would cause a derangement of lipid transport. The efficient hepatic removal of the enzyme may thus serve an important physiological purpose in keeping the blood levels of this enzyme low.

Animals↗
PubMed1979

Colipase enhances hydrolysis of dietary triglycerides in the absence of bile salts.

This study explores how dietary lipids are digested when intraduodenal bile salts are low or absent. Long-chain triglycerides emulsified with phosphatidylcholine were found to be hydrolyzed very slowly by pancreatic lipase alone, as if the surface layer of phospholipids enveloping the triglycerides impeded the action of the enzyme. Colipase enhanced triglyceride hydrolysis severalfold, both when added before or after the lipase. Hydrolysis became even more rapid when the emulsion was first incubated with pancreatic phospholipase. Hydrolysis of long-chain triglycerides was also severely impeded when other proteins were added to the system, probably because they adsorbed to the oil-water interface of the emulsion droplets. It was previously known that bile salts can relieve such inhibition, presumably by desorbing the adsorbed proteins. Colipase was found to enhance hydrolysis severalfold in a dose-dependent manner even in the absence of bile salts, i.e., it could partially or completely relieve the inhibition depending upon the amount and the type of inhibitory protein added to the system. Prior exposure of a protein-coated triglyceride emulsion to another lipase also enhanced the rate at which pancreatic lipase could then hydrolyze the lipids. Most dietary triglycerides are probably presented for intestinal digestion in emulsions covered by proteins and/or phospholipids. These emulsions would be hydrolyzed slowly by pancreatic lipase alone. However, through the action of the lipase in stomach contents and of pancreatic phospholipase and through the lipolysis-promoting effects of collipase, these triglycerices can be rather efficiently hydrolyzed, even in the absence of bile salts.

Animals↗
PubMed1979

Very low density lipoprotein. Fate of phospholipids, cholesterol, and apolipoprotein C during lipolysis in vitro.

In this study we have determined the fate of phospholipids, cholesterol, and apolipoprotein C during lipolysis of rat plasma very low density lipoprotein (rat VLDL). The experiment was carried out in vitro with lipoprotein lipase purified from bovine milk, VLDL labeled with [(14)C]palmitate, [(3)H]cholesterol, [(32)P]phospholipids, and (125)I-labeled apolipoprotein C and in plasma-devoid systems. Triglyceride hydrolysis ranged between 0 and 98.6%. [(32)P]Phospholipids, unesterified [(3)H]cholesterol, and (125)I-labeled apolipoprotein C were removed from the VLDL (d < 1.019 g/ml) during lipolysis. About one-third of the [(32)P]phosphatidylcholine was hydrolyzed to lysolecithin, and was transferred to the fraction d > 1.21 g/ml. The other two-thirds of the phospholipids were removed unhydrolyzed, mainly to the fraction d 1.04-1.21 g/ml. With the progression of the lipolysis, unesterified [(3)H]cholesterol was removed from VLDL at increasing rates, predominantly to the fraction d 1.04-1.21 g/ml. (125)I-Labeled apolipoprotein C removed from the VLDL partitioned between the fraction of d 1.04-1.21 g/ml and d > 1.21 g/ml. Negative-staining electron microscopy of the fraction d 1.04-1.21 g/ml (containing phospholipids, unesterified cholesterol, and apolipoprotein C) revealed many discoidal lipoproteins. [(3)H]Cholesteryl esters remained associated with the VLDL even when 70-80% of the triglycerides were hydrolyzed. These observations suggest that during in vitro lipolysis of VLDL, surface constituents leave the lipoprotein concomitantly with the hydrolysis of core triglycerides. The process of removal of surface constituents is independent of the presence of an acceptor lipoprotein and may occur in the form of a surface-fragment particle. -Eisenberg, S., and T. Olivecrona. Very low density lipoprotein. Fate of phospholipids, cholesterol, and apolipoprotein C during lipolysis in vitro.

Animals↗
PubMed1978

Comparison of the phospholipase activity of bovine milk lipoprotein lipase against rat plasma very low density and high density lipoprotein.

The hydrolytic activity of a lipoprotein lipase from bovine milk against triacylglycerol and phosphatidylcholine of rat plasma very low density lipoprotein was determined and compared to that against phosphatidylcholine of high density lipoprotein. 85--90% of the triacylglycerol in very low density lipoprotein were hydrolyzed to fatty acids and 25--35% of the phosphatidylcholine to lysophosphatidylcholine. High density lipoprotein phosphatidylcholine was only minimally susceptible to the enzyme. Even with high amounts of enzyme and prolonged incubation periods, lysophosphatidylcholine generation did not exceed 2--4% of the original amounts of labeled phosphatidylcholine in the high density lipoprotein. We conclude that phospholipids in high density lipoprotein are not substrates for the phospholipase activity of this lipoprotein lipase. These observations suggest that factors other than the presence of apolipoprotein C-II and of glycerophosphatides are of importance for the activity of lipoprotein lipases.

Animals↗