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G Nalbone

Publications and source records attributed to G Nalbone.

At least 55 records · Page 3Linked to original sources
PubMed1987

Effect of dietary lipids on the lipid composition and phospholipid deacylating enzyme activities of rat heart.

Rats were fed lard-enriched (17%) or corn oil-enriched (17%) diets and were compared with rats fed a low fat (4.5%) diet. Cardiac protein, DNA, phospholipid (PL) and fatty acid (FA) compositions were analyzed. Neutral phospholipase A, lysophospholipase and creatine kinase activities in the membrane and cytosolic compartments were also investigated. No significant modification of cardiac protein, DNA nor PL was observed among the three groups. Some alterations appeared in the FA composition. A lard-enriched diet induced a significant increase of 22:5n-3 and 22:6n-3 in heart phosphatidylcholine (PC) and phosphatidylethanolamine (PE), whereas a linoleic acid-rich diet induced a specific increase of 22:4n-6 and 22:5n-6 in these two major PL. Compared to rats fed the low fat diet, membrane-associated phospholipase A activity, measured by endogenous hydrolysis of membrane PC and PE, showed a significant increase (+45%) for both PL in rats fed corn oil. However, the activity of membrane-associated phospholipases, measured with exogenous [1-14C]dioleoyl PC, was not different among the three groups of rats. Cytoplasmic activity was decreased in rats fed corn oil, and lysophospholipase and creatine phosphate kinase activities were not significantly affected by diet. FA modification of the long chain n-6 FA induced by corn oil may be responsible for the observed increase in phospholipase activity. Physiological implications are suggested in terms of membrane degradation and prostaglandin production.

Animals↗
PubMed1987

Phospholipase A2 activity of rat stomach.

Phospholipase A activity in rat stomach wall and in gastric content was studied using [1-14C]dioleoylphosphatidylcholine as substrate. The optimum activity of the stomach wall was found to take place at pH 7.0. During optimal phospholipase action about 40% of the [1-14C]oleic acid released was due to an active intracellular lysophospholipase. The gastric phospholipase required 5 mM Ca2+ for full activity and is inhibited by EDTA. It specifically hydrolyzed the sn-2 position of the phospholipid molecule. The enzyme was heat labile and inactivated by acidification at pH 3.0. The gastric content enzyme had a lower specific activity and an optimum pH of 8.0. It was heat stable and was not inactivated by acidification. These results indicate that gastric content phospholipase A is of pancreatic origin, via a duodenal reflux. By ligating the stomach we were able to further confirm that the gastric wall phospholipase was different from that of the gastric content. It originated from the stomach mucosa. Subcellular fractionation suggests that the gastric phospholipase A2 is essentially bound to the plasma membrane. About 6% of the activity was found to be soluble. Biopsies of human gastric mucosa displayed a phospholipase A activity which had similar properties to that of rat gastric enzyme. The physiological function of this enzyme is discussed in terms of prostaglandin synthesis via the release of arachidonic acid.

Animals↗
PubMed1987

Intracellular phospholipase activity in rat heart: comparison between endogenous and exogenous substrates.

Two methods were used to estimate the intracellular phospholipase activity in rat heart: one using exogenous radioactive substrate dispersed as unilamellar vesicles; the other using endogenous membrane hydrolysis and subsequent phospholipid and lysophospholipid separation by high-performance liquid chromatography and quantification by phosphorus determination. We found that the endogenous method provided a higher hydrolysis rate than the exogenous method and that phosphatidyl ethanolamine was a better substrate than phosphatidyl choline.

Animals↗
PubMed1986

Partial characterization of rat heart cytosolic phospholipase A1 and demonstration of essential sulfhydryl groups.

The cytosol of rat heart has been previously shown to contain phospholipase A activity in substantial amounts. This paper describes the isolation and partial purification of rat heart cytosolic phospholipase A. After homogenization of rat heart followed by centrifugation to remove membraneous material, the phospholipase A activity was isolated by ammonium sulfate precipitation and further purified by gel permeation chromatography with Sephadex G-100 in the presence of 5 mM taurodeoxycholate. Two peaks were isolated: a minor peak at the void volume and major peak corresponding to a molecular weight of 45,000. The molecular weight observed in HPLC gel permeation chromatography experiments was also Mr 45,000 and was not significantly affected by the nature of the detergent used. Phospholipase A was purified 77-fold over the crude cytosol. Further purification could not be attained due to lability of the phospholipase A activity. The enzyme is a phospholipase of the A1 type which does not require Ca2+ and lacks lipase or transacylase activity. It is unusual for the phospholipases A described to date, since it is inhibited by thiol reagents and is protected by beta-mercaptoethanol, suggesting the presence of essential sulfhydryl residues.

Animals↗
PubMed1986

A quantitative dynamic concept of the interphase partition of lipids: application to bile salt-lecithin-cholesterol mixed micelles.

A system is proposed for a quantitative classification of lipids, based on interphase partition coefficients. This system enables calculation of exchanges of lipid molecules between phases. The mass/volume chemical unit mol X cm-3, strictly derived from the CGS system, is used, thus simplifying mathematical relations. Applied to bile salt-lecithin-cholesterol mixed micelles, this dynamic concept gives new insight into the variations of physico-chemical parameters. Experimental results obtained with the glycodesoxycholate and the taurocholate show a striking difference in partition coefficients between aqueous and mixed bile salt-lecithin interfacial phases. A new model applying triangular co-ordinates to a bile salt-lecithin-cholesterol mixed lipid phase is described.

Bile Acids and Salts↗
PubMed1985

Hydrolysis of intralipid by pancreatic lipase and phospholipase A2-gel filtration studies.

Intralipid was incubated with pancreatic lipase (EC 3.1.1.3) and/or phospholipase A2 (EC 3.1.1.4) at two bile salts/phosphatidylcholine molar ratios and at two different triglyceride hydrolysis rates using various amounts of lipase. Incubations were studied by gel filtration. Results show: During lipase action, three phases of lipids coexist: an emulsified phase, a micellar phase and an intermediate heavy phase sized between the two others. The equilibrium between each phase is dependent upon the bile salts concentration. Under these conditions, pancreatic lipase was at 60% bound to the emulsified phase, whereas pancreatic phospholipase A2 was bound at 94% to the micellar phase.

Animals↗
PubMed1985

Purification of the human anionic polypeptide fraction of the apo-bile lipoprotein complex by zonal ultracentrifugation.

The two main proteic constituents of the human Apo-bile lipoprotein complex (BLC), i.e., the anionic polypeptide fraction (APF) and the IgA fragments, were separated by preparative zonal ultracentrifugation using a sucrose gradient containing 1.5 mM glycodesoxycholate. The purification of the APF was verified by sodium dodecyl sulphate (SDS) polyacrylamide gel electrophoresis and immunology, and its amino acid composition then was determined. This procedure was used to obtain a polyclonal antiserum directed solely against the APF.

Amino Acids↗
PubMed1985

Effects of dietary fibers and cholestyramine on the activity of pancreatic lipase in vitro.

Most experiments were conducted in the presence of human gallbladder bile; colipase and pancreatic lipase were purified using porcine pancreas. The adsorption of bile salts, phospholipids and cholesterol from the bile, together with that of pancreatic lipase was measured on wheat bran, cellulose, hemicellulose (xylan), slightly methylated pectin (42%) and cholestyramine. In contrast to cholestyramine which intensively binds biliary lipids (61.7-81.7%) and pancreatic lipase (47.5%), the fibers studied only had a low adsorbent power. The direct influence of these fibers and of cholestyramine at concentrations ranging from 0-5% on lipase activity was measured at constant pH, using two conventional assay systems, long chain triglycerides and tributyrin. In the presence of human bile and colipase, a drastic reduction in triglyceride hydrolysis by lipase was observed with cholestyramine (loss of 66-82%) and wheat bran (loss of 77-94%) at 1% concentration. The other fibers did not have any marked effects on enzyme activity. The use of a radio labeled lipase made it possible to demonstrate that the inhibitory effect of bran on enzyme activity was independent of adsorption phenomena on bran. The fraction of bran that can be solubilized in the aqueous phase, in fact, induced this reduction in activity. The presence of protein inhibitor in bran may be responsible for the reduction in pancreatic lipase activity.

Animals↗
PubMed1985

Subcellular localization of the phospholipases A of rat heart: evidence for a cytosolic phospholipase A1.

During myocardial ischemia increased levels of lysoglycerophospholipids have been reported which may be deleterious to myocardial function. Phospholipases are presumed to be important in the regulation of this process. To further quantify and characterize the activity of heart phospholipases, we carried out a systematic analysis of phospholipase A activity in rat heart subcellular fractions isolated by the method of Palmer et al. (J. Biol. Chem. 1972. 262: 8731-8739). Neutral phospholipase A was recovered predominately in the cytosolic (soluble) fraction which represented 46% of recovered activity, while the microsomal and subsarcolemmal mitochondrial fractions represented 15% and 12% of the total recovered activity, respectively. Cytosolic phospholipase A differed from the two principal membrane-bound phospholipases A in its pH dependence and apparent Km for substrate. The cytosolic enzyme had a Km (apparent) for dioleoylphosphatidylcholine of 0.07 mM versus 0.28-0.33 mM for the membrane-associated phospholipases A. Acid phospholipase A activity had a subcellular distribution consistent with a lysosomal localization. Lysophospholipase was found principally in the cytosolic, microsomal, and the subsarcolemmal and interfibrillar mitochondrial fractions where it represented 46, 17, 6.3, and 6.9% of the recovered activity, respectively. The positional specificity of the respective phospholipases was assessed. This analysis was complicated by the fact that in heart, lysophospholipase has an observed Vmax 3.6- to 4.5-fold greater than that of phospholipase A in the various subcellular fractions. Equations were derived to obtain corrected values for the activity of phospholipases A1 and A2. Using this method we found that the cytosolic and lysosomal fractions contained phospholipase A1, while the mitochondrial fractions contained primarily phospholipase A2. In heart microsomes, the positional specificity of phospholipase A could not be determined because lysophospholipase activity was very high and lysophosphatidylcholine did not accumulate.

Animals↗
PubMed1983

Immunohistochemical localization of the apoproteins of the bile lipoprotein complex in the human intestine.

The human bile lipoprotein complex includes an apoprotein fraction of IgA fragments and an acidic polypeptide tightly bound to bile cholesterol and phosphatidylcholines. The fate of the intestinal bile lipoprotein complex was immunohistochemically studied. Its localization in the human duodenum is consistent with selective capture or synthesis. The result of both might be the presence of bile apoprotein in the bloodstream. These two mechanisms may explain the cross-reaction between the lipoprotein complex apoprotein and the high density lipoprotein.

Apolipoproteins↗
PubMed1983

Adsorption of pancreatic (pro)phospholipase A2 to various physiological substrates.

The adsorption of pancreatic phospholipase was studied in vitro in the presence of egg yolk lipoprotein emulsion, Intralipid emulsion, and milk fat globules. When the emulsions are incubated with bile salts, the latter dissociate a considerable fraction of the phospholipids initially associated with the emulsions, leading to the coexistence of an emulsified phase and a phase of mixed micelles. After the addition of pancreatic phospholipase A2, gel filtration shows that the enzyme was more than 90% bound to mixed micelles, regardless of the type of emulsion used. Comparable results were obtained by replacing the bile salts with human gallbladder bile. In parallel, pancreatic zymogen was never found to be bound to any of the lipid structures present (emulsion or mixed micelles). When the catalytic site of pancreatic phospholipase A2 was blocked with 4-bromophenacylbromide, there was no fixation on mixed micelles. Fixation was restored by the presence of lysolecithins and fatty acids in the incubation mixtures. The partial transformation of all emulsified substrates to mixed micelles by bile salts in vivo would thus lead to optimum activity of pancreatic phospholipase A2.

Adsorption↗
PubMed1982

Comparative immunohistochemical localization of IgA and of the IgA part of the bile lipoprotein complex in dog and rat liver.

In bile, phospholipids and cholesterol were found in close association with an apoprotein fraction which cross-reacted to antiserum anti-IgA. In order to determine the origin of the IgA part of the apo bile lipoprotein complex and to establish its relationship with IgA, th localizations of these two components in rat and in dog livers were compared. Two immunohistochemical methods were used. Whereas IgA was found on the sinusoidal surface of the hepatocytes, in cytoplasmic particles and in bile canaliculi, the IgA part of the apo bile lipoprotein complex was only detected in the bile canaliculi, and in particles which presented the same pattern of location as lysosomes. These results suggest that the IgA part of the apo bile lipoprotein complex could originate from the transit of a part of the internalized IgA via the lysosomal compartment of the hepatocytes.

Animals↗
PubMed1981

Interaction of immunoglobulins and lipids in human gallbladder bile.

The lipoprotein complex from human gallbladder bile was challenged with anti-IgA and anti-IgG antisera in order to determine whether the apolipoprotein complex isolated from the detergent-free form of bile lipoprotein contains IgA and IgG. The apolipoprotein complex indeed crossreacts with anti-IgA and anti-IgG. In addition, the interactions of IgA and IgG with lipids were studied by ultracentrifugation and gel chromatography to determine whether these interactions occur in human bile.

Bile↗
PubMed1980

Pancreatic phospholipase A2 hydrolysis of phosphatidylcholines in various physicochemical states.

Bile salts-phosphatidylcholines-cholesterol mixed micelles, native bile, egg yolk and intralipid emulsions were used as pancreatic phospholipase A2 (EC 3.1.1.4) substrates. The enzyme activity depends on the bile salt/phosphatidylcholine molar ratio. The enzyme had a low specific activity on bile phosphatidylcholines, because of the existence in native bile of a high bile salt/phosphatidylcholine molar ratio generating unfavorable conditions of hydrolysis, as demonstrated with mixed micelles. However when the bile salt/phosphatidylcholine molar ratio from bile was decreased to 2 : 1, enzyme activity increases up to an optimum. This optimal activity was about one third that observed when the substrate was mixed micelles. Under these optimal conditions a simultaneous hydrolysis of intralipid and bile phosphatidylcholine mixture shows comparable initial hydrolysis rates. During an extended incubation, however, nearly all intralipid phosphatidylcholines and only half the bile phosphatidylcholines were hydrolyzed by pancreatic phospholipase A2. Bile salts mixture or native bile desorb a portion of the phosphatidylcholines from the intralipid emulsion in optimally hydrolysable bile salts phosphatidylcholines mixed micelles. These micelles bind about 85% of the enzyme indicating that hydrolysis occurs primarily in the micellar phase. These results are discussed in terms of fat lipolysis in vivo.

Animals↗
PubMed1980

The influence of bile salts and bile lipoprotein complex on pancreatic lipase hydrolysis of monomolecular films.

We report a new technique which allows us to follow the lipolysis of monomolecular films in the presence of bile salts by using a 'zero-order' trough (Verger, R. and de Haas, G.H. (1973) Chem. Phys. Lipids 10, 127). The effects of bile salts, the bile lipoprotein complex and colipase on pancreatic lipase hydrolysis of rac-1,2-didodecanoylglycerol films were studied at different surface pressures. Taking into account previous studies, lipase activity was interpreted as a function of its degree of binding to the bile lipoprotein complex.

Animals↗
PubMed1980

Effect of bile lipids on the adsorption and activity of pancreatic lipase on triacylglycerol emulsions.

Emulsions of natural triacylglycerols obtained with different shear forces were used to study lipase adsorption and lipolysis. The influence of the bile lipoprotein complex on these two processes was determined. Optimal lipase activity was observed to occur with a given phospholipid : triacylglycerol ratio. This ratio depended on the degree of triacylglycerol emulsification and was accompanied by maximal adsorption of the bile lipoprotein complex. These results support our previous model for pancreatic lipolysis under physiological conditions, according to which colipase controls lipase binding to the bile lipoprotein complex and the resulting association directs enzyme adsorption to the acylglycerol particle (Lairon, D., Nalbone, G., Lafont, H., Léonardi, J., Domingo, N., Hauton, J.C. and Verger, R. (1978) Biochemistry 17, 5263--5269).

Adsorption↗