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Biomedical subjects

R L Jackson

Publications and source records attributed to R L Jackson.

At least 163 records · Page 9Linked to original sources
PubMed1980

Preparation and properties of immobilized lipoprotein lipase.

Purified bovine milk lipoprotein lipase has been covalently attached to CH-Sepharose with water-soluble carbodiimide. The immobilized enzyme retained enzymic activity and was stimulated 7-fold by the addition of human apolipoprotein C-II. Both [3H]heparin and 125I-labeled apolipoprotein C-II bound to the immobilized enzyme; unlabeled heparin and apolipoprotein C-II competed for binding of their respective labeled compounds. Apolipoprotein C-II did not compete for binding of [3H]heparin and vice versa. Human apolipoprotein C-III did not bind to the immobilized enzyme nor did it compete for apolipoprotein C-II binding. We conclude from these studies that both apolipoprotein C-II and heparin interact with immobilized lipoprotein lipase and that they have different binding sites.

Animals↗
PubMed1980

Incorporation of dipalmitoyl phosphatidycholine into human plasma low density lipoproteins: effects on composition and structure.

Bovine liver phosphatidylcholine exchange protein was used to transfer di[14C]palmitoyl phosphatidylcholine from sonicated vesicles to human plasma low density lipoproteins (LDL). The incorporation of di[14C]-palmitoyl phosphatidylcholine into LDL was associated with an increased percentage of total phospholipid and increased lipid rigidity as shown by an increase in the fluorescence polarization of 12-(9-anthroyloxy)-stearic acid and 1,6-diphenyl-1,3,5-hexatriene.

Animals↗
PubMed1980

Dansyl phosphatidylethanolamine-labeled very low density lipoproteins. A fluorescent probe for monitoring lipolysis.

The fluorescent phospholipid dansyl phosphatidylethanolamine (DPE) (dansyl, 5-dimethylaminonaphthalene-1-sulfonyl) was incorporated into very low density lipoproteins (VLDL) to form DPE-VLDL. The addition of milk lipoprotein lipase to DPE-VLDL in the presence of albumin resulted in a greater than 3-fold fluorescence increase and a 20 nm blue shift in the wavelength of the emission maxima of the dansyl fluorophore. The lipoprotein lipase-induced fluorescence changes occurred concomitantly with the release of free fatty acids from VLDL. Lipoprotein lipase did not produce fluorescence changes in DPE incorporated into either low or high density lipoproteins. The rate of fluorescence increase in DPE-VLDL was maximal at 37 degrees C, dependent on the concentration of lipoprotein lipase and VLDL, and followed typical Michaelis-Menten kinetics with a Km of 1.0 for lipoprotein lipase. Both the initial rate and the total fluorescence increase correlated well (r = 0.98 and 0.95) with the release of free fatty acids. We conclude that the lipoprotein lipase-induced fluorescence increases in DPE-VLDL provide an accurate, convenient, and the only noninvasive means of following continuously the lipolysis of human VLDL.

Animals↗
PubMed1980

Mechanism of action of milk lipoprotein lipase at substrate interfaces: effects of apolipoproteins.

The mechanism of action of bovine milk lipoprotein lipase was studied by using a monomolecular film of 1,2-didecanoylglycerol. The apparent rate of hydrolysis of diglyceride increased with increasing surface pressures above 12 mN/m; the enzyme was inactive at pressures less than 12 mN/m. We have measured the effects of four plasma apolipoproteins (apoC-II, apoC-III, apo-I, and apoE), bovine serum albumin, porcine pancreatic colipase, heparin, and NaCl on the kinetics of lipid hydrolysis. At a surface pressure of 15 mN/m, all of the proteins, with the exception of colipase, gave increased enzyme activity compared to lipase alone; apoC-II gave maximal activation. At 25 mN/m, apoC-II at concentrations of less than 0.25 microgram/mL showed a specific activation, whereas the other proteins had no effect. Heparin activated at both high and low surface pressures; NaCl had little or no effect in this system. At a higher concentration of apoC-II (0.50 microgram/mL), the apoprotein inhibited the enzyme. The addition of apoC-III, apoA-I, or apoE (final concentration 0.25 microgram/mL), but not albumin or colipase, to apoC-II (0.25 microgram/mL) caused an increase in surface pressure of 5-6 mN/m and an apparent rate which was less than half that found for lipase alone, suggesting that all of the apoproteins inhibit the apoC-II specific activation.

Animals↗
PubMed1980

Opiate antagonists and long-term analgesic reaction induced by inescapable shock in rats.

Five experiments examined the influence of opiate antagonists on both the short-term analgesic reaction resulting 30 min after exposure to inescapable shock and the long-term analgesic reaction resulting after reexposure to shock 24 hr after inescapable shock exposure. Experiment 1 showed that the long-term analgesic reaction could be reduced by administration of naltrexone prior to exposure to inescapable tail shock. Experiment 2 showed that the reduction in the long-term analgesic reaction produced by naltrexone was dose-dependent. Experiment 3 showed that the long-term analgesic reaction could also be reduced by administration of naltrexone prior to reexposure to shock. Experiment 4 showed that the long-term analgesic reaction could be reduced by administration of large dose of naloxone prior to reexposure to shock. Experiment 5 showed that the short-term analgesic reaction was reduced by naltrexone administered prior to inescapable shock. Some implications of these results for the biochemical substrates of both learned helplessness and stress-induced analgesia are discussed.

Animals↗
PubMed1980

Glucose infusions increase plasma levels of amyloid proteins in high density lipoproteins.

Malmendier et al. (4) have described six apoproteins from human plasma high density lipoproteins (HDL) which were isolated from patients given an intravenous infusion of 10% glucose. Inspection of their amino-terminal sequences indicate that Malmendier et al. have isolated various forms of serum amyloid AA. Since amyloid is present in patients with various chronic diseases which are associated with decreased HDL levels, we suggest that there is a relationship between amyloid and HDL.

Amino Acid Sequence↗
PubMed1980

Learned helplessness, inactivity, and associative deficits: effects of inescapable shock on response choice escape learning.

These experiments explored whether exposure to inescapable shock produces a subsequent deficit in the organism's propensity to associate its behavior with shock termination. Previous experiments are incapable of resolving this question because they confound reduced associability and decreased activity. Four experiments examined the effects of inescapable shock on the acquisition of Y-maze escape. Here, escape is accomplished by choosing the correct response from two available alternatives rather than by simple locomotion as in a shuttle box. By itself, reduced activity should not produce inaccurate choices, only slow choices. Experiment 1 found that inescapable shock produced slow learning of the correct choice for escape, even though active choices occurred on every trial. Further, the speed and accuracy of choice were not correlated. The second experiment showed that the choice escape learning deficit was produced by the inescapability of the shocks. Experiment 3 demonstrated that the choice accuracy of inescapably shocked rats was not improved by increases in Y-maze shock intensity, even though speed of responding was increased. The final experiment revealed that the effects of inescapable shock on Y-maze acquisition did not dissipate across a 1-wk period.

Animals↗
PubMed1980

Purification and properties of bovine aortic lipoprotein lipase.

Lipoprotein lipase of bovine aortic intima has been purified to homogeneity by affinity chromatography on heparin-Sepharose. As determine by polyacrylamide gel electrophoresis in sodium dodecyl sulfate, the purified enzyme had a molecular weight of approximately 60,000, required apolipoprotein C-II for activity and was inhibited by 1.0 M NaCl. Optimum lipolytic activity was in the pH range of 8.0-8.5. Bovine skimmed milk lipoprotein lipase was also purified and its properties compared to those of the aortic enzyme. Based on these comparative studies, we conclude that bovine aortic and milk lipoprotein lipase have similar properties.

Animals↗
PubMed1980

Influence of an atherogenic diet on the structure of swine low density lipoproteins.

Five groups of three swine each were fed a basal diet supplemented with 15% tallow and either 0.0, 1.0, 1.5, 2.0%, or 2.5% cholesterol. The animals were studied over a period of 9 weeks to observe changes in plasma lipids and low density lipoproteins (LDL). At the end of the study period, LDL was analyzed by rate zonal ultracentrifugation, characterized chemically, and examined by differential scanning calorimetry. Within 3 weeks of initiation of the cholesterol-supplemented diets, there was an increase in the plasma levels of cholesterol and total LDL. LDL from swine fed the basal diet and the basal diet plus 1.0% cholesterol appeared in two LDL populations (LDL1 and LDL2) when analyzed by rate zonal ultracentrifugation. After diets containing 1.5, 2.0, and 2.5% dietary cholesterol, there was an increase in the mean flotation rate of total LDL which shifted to a lower density. LDL1 from the high cholesterol diets had a decreased triglyceride content when compared to those of the low cholesterol diets. When examined by differential scanning calorimetry, the LDL1 from the animals fed at least 1.5% cholesterol had phase transitions above body temperature, whereas the LDL from those fed 0 and 1.0% cholesterol had phase transitions below 37 degrees C. In contrast, the thermal behavior and fatty acid compositions of the extracted cholesteryl esters of the LDL obtained after the five different diets were not remarkably different. Since LDL triglyceride and cholesteryl esters are predicted to coexist in a common phase in the LDL core, the different thermal behavior of the LDL obtained after diets with different cholesterol contents is due to differences in triglyceride content which are a secondary effect of cholesterol-feeding. From these data we conclude that dietary cholesterol increases plasma LDL content, decreases LDL triglyceride content, and alters the particle structure. These changes in lipoprotein structure may contribute to the known development of atherosclerosis in cholesterol-fed swine.

Animals↗
PubMed1979

Exchange of phospholipids between unilamellar vesicles of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine and plasma very low density lipoproteins.

Purified phosphatidylcholine exchange protein from bovine liver was used to exchange [14C]dipalmitoyl phosphatidylcholine from sonicated vesicles to human plasma very low density lipoproteins (VLDL). The exchange of [14C]-dipalmitoyl phosphatidylcholine for VLDL phospholipids was temperature dependent and linear with respect to time and amount of exchange protein. In the absence of the exchange protein, less than 10% of the [14C]dipalmitoyl phosphatidylcholine was transferred. At an initial weight ratio of [14C]-dipalmitoyl phosphatidylcholine vesicles to VLDL phospholipid (1.2 mg) of 2.2, the exchange protein (14 microgram) replaced 55% of the VLDL phospholipids with [14C]dipalmitoyl phosphatidylcholine in 15 min; VLDL protein and cholesterol content were unaltered. From these studies we conclude that the exchange protein is a useful method to alter the phospholipid composition of VLDL under conditions such that there is minimal perturbation of the lipoprotein.

Androgen-Binding Protein↗
PubMed1979

Interaction of plasma apolipoproteins with lipid monolayers.

The monolayer technique has been used to study the interaction of lipids with plasma apolipoproteins. Apolipoprotein C-II and C-III from human very low density lipoproteins, apolipoprotein A-I from human high density lipoproteins and arginine-rich protein from swine very low density lipoproteins were studied. The injection of each apoprotein underneath a monolayer of egg phosphatidy[14C]choline at 20 mN/m caused an increase in surface pressure to approximately 30 mN/m. With apolipoprotein C-II and apolipoprotein C-III there was a decrease in surface radioactivity indicating that the apoproteins were removing phospholipid from the interface; the removal of phospholipid was specific for apolipoprotein C-II and apolipoprotein C-III. Although there was a removal of phospholipid from the monolayer, the surface pressure remained constant and was due to the accumulation of apoprotein at the interface. The rate of surface radioactivity decrease was a function of protein concentration, required lipid in a fluid state and, of the lipids tested, was specific for phosphatidylcholine. Cholesterol and phosphatidylinositol were not removed from the interface. The addition of 33 mol% cholesterol to the phosphatidylcholine monolayer did not affect the removal of phospholipids by apolipoprotein C-III. The addition of phospholipid liposomes to the subphase greatly facilitated the apolipoprotein C-II-mediated removal of phospholipid from the interface. Although apolipoprotein A-I and arginine-rich protein gave surface pressure increases, phospholipid was only slightly removed fromthe interface by the addition of liposomes. Based on these findings, we conclude that the apolipoproteins C interact specifically with phosphatidylcholine at the interface. This interaction is important as it relates to the transfer of the apolipoproteins C and phospholipids from very low density lipoproteins to other plasma lipoproteins. The addition of human plasma high density lipoproteins or very low density lipoproteins to the subphase increased the apolipoprotein C-mediated removal of phosphatidyl[14C]choline from the interface 3--4 fold. Low density lipoproteins did not affect the rate of decrease. During lipolysis of very low density lipoproteins to the subphase increased the apolipoprotein C-mediated removal of with the lipid monolayer. Lipolysis experiments were performed in a monolayer trough containing a surface film of egg phosphatidyl[14C]choline and a subphase of very low density lipoproteins and bovine serum albumin. Lipolysis was initiated by the addition of purified milk lipoprotein lipase to the subphase. As a result of lipolysis, there was a decrease in surface radioactivity of phosphatidylcholine. The pre-addition of high density lipoproteins decreased the rate of decrease in surface radioactivity...

Animals↗