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Biomedical subjects

J Polonovski

Publications and source records attributed to J Polonovski.

At least 91 records · Page 5Linked to original sources
PubMed1981

Redistribution of apolipoproteins C removed from human very low density lipoprotein during in vitro lipolysis by lipoprotein lipase.

In order to localize the labelled apolipoproteins C removed from Very Low Density Lipoproteins (VLDL) during lipolysis by lipoprotein lipase, we used human VLDL labelled with 125I-labelled apolipoproteins C and employed density gradient ultracentrifugation to analyze lipolytic products. Triacylglycerol hydrolysis occurs when albumin is present even in the absence of serum or High Density Lipoproteins (HDL). In this case, apolipoproteins C were found to be located in several fractions, in different density regions. When either HDL or serum were present in the incubation medium, the removed apolipoproteins C were recovered in only one main fraction in the high density region (1.10 g/ml). Incubations in the presence of either HDL2 or HDL3 gave quite similar results.

Apolipoproteins↗
PubMed1981

[Metabolism of cholesterol in normal hamster fibroblasts and those transformed by the SV 40 virus. Effect of low density lipoproteins].

The amount of cholesterol and the percentage of esterified cholesterol were increased in transformed cells. The cholesterol synthesis from [14C] sodium acetate was reduced and cholesteryl oleate uptake increased by 3 fold in transformed cells. The activity of acyl coenzyme A-cholesterol-acyltransferase, measured in situ was also increased in transformed cells. Studies with 125I-LDL pointed out an increase of binding, and especially of internalization of LDL by transformed cells. Finally, long term culture in a lipoprotein-deficient medium showed that transformed cells exhibited a higher ability (tested by growth rate and cholesterol synthesis) to adapt themselves to lipid depletion.

Animals↗
PubMed1980

[Phospholipase A2 activity in rat serum. Association of two proteins (author's transl)].

In the rat, blood coagulation is accompanied by activation of a plasma phospholipase A2 due to a factor contained in blood platelets and released in plasma by platelet lysis. This activity can be obtained in vitro by treating plasma devoid of platelets with a platelet lysate. The results reported in this communication show the activity of serum phospholipase to result from an association of two proteins, inactive when isolated, one originating from plasma, the other from platelets, which can be broken down by fractionation on a column of Blue Sepharose CL-6B.

Animals↗
PubMed1980

Acylation of endogenous phospholipids and added lysoderivatives by rat liver plasma membranes.

Phospholipid acyltransferase activities of plasma membranes have been investigated with various acyl-CoA thioesters (palmitoyl, stearoyl, oleoyl, linoleoyl and arachidonoyl) with and without added lysoderivatives. Different patterns of incorporation were observed for each acyl-CoA into endogenous phosphatidylcholine and phosphatidylethanolamine. The turnover rates calculated with tracer amounts of 10 microM acyl-CoA thioesters were five times faster for the polyunsaturated than for the saturated acyl moieties of phosphatidylethanolamine and phosphatidylcholine. Arachidonoyl-CoA was the best acyl donor at low concentrations and the maximal turnover rate was observed at about 25 microM. No saturation appeared at up to 100 microM linoleoyl-CoA. Linoleoyl-CoA transacylase acylated the lyso-compounds in the following order: lysophosphatidylcholine greater than lysophosphatidylserine and lysophosphatidylinositol, while lysophosphatidylethanolamine inhibited linoleate incorporation into the phosphatidylethanolamine itself. Linoleoyl-CoA transacylation was not affected by the fatty acyl moiety at the 1-position of the lysophosphatidylcholine. The results support the view that the plasma membrane acyltransferase activity might contribute to the formation of bile phosphatidylcholines.

Acylation↗
PubMed1980

[Activation of blood phospholipases by proteins present in crude trypsin extracts].

Blood phospholipase activity in increased by crude trypsin (Sigma). This activity is not induced by trypsin itself but by some proteins contained in the extract and isolated from trypsin by G 75 Sephadex filtration. Purified trypsin or pure trypsin (Fluka, Merck, Boehringer) do not increase phospholipase activity.

Chromatography, Gel↗
PubMed1980

[Inhibition by the high density lipoprotein HDL2 and HDL3 of DNA and sterol biosynthesis in human lymphocytes stimulated with concanavalin A].

Lipoproteins HDL2 and HDL3 inhibit DNA synthesis and sterol synthesis in human Con A-stimulated lymphocytes cultured in a medium supplemented with 20 per cent lipoprotein deficient serum. On the basis of the amount of proteins added, HDL2 is more efficient on DNA and sterol synthesis than HDL3 and less efficient than LDL. However, on the basis of the amount of cholesterol added, the inhibition of sterol synthesis induced by these three lipoproteins is not significantly different. At all concentrations of these three lipoproteins, the inhibition of sterol synthesis is higher than the inhibition of DNA synthesis.

Cells, Cultured↗
PubMed1980

[Presence and isolation of 2 lipoproteins immunologically related to apolipoprotein A I in human serum].

Very high density lipoproteins d : 1.23--1.25 g/ml (VHDL2) have been isolated from human serum by preparative ultracentrifugation. They contain 80 per cent proteins and 20 per cent lipids. Lipids are mainly phospholipids (80 per cent). The proportion of lysolecithin (50 per cent) is higher than that of lecithin (40 per cent). The quantity of cholesterol is low, the free cholesterol: total cholesterol ratio is 0.35. VHDL2 consisted principally in lipoprotein D and two lipoproteins immunologically apparented to apolipoprotein A I, called LP A I1 and LP A I2. The LP A I1 has a molecular weight slightly higher and a hydrated density lower than that of LP AI2. Our experiments suggest that LP A I1 exists in the serum before ultracentrifugation while LP A I 2 comes from HDL degradation during ultracentrifugation. The immunological heterogeneity of apo A I forming different protein-lipid complexes is discussed.

Apolipoproteins↗
PubMed1980

Purification of an anti-lipoprotein lipase antiserum.

Lipoprotein lipase is an enzyme difficult to isolate in pure form and, until now, the antisera prepared against it have not been monospecific. The present experiments show how a crude antiserum prepared with bovine milk lipoprotein lipase, can be made more specific through suitable adsorption. The crude antiserum was prepared by injecting milk lipoprotein lipase prepared by heparin Sepharose affinity chromatography. Immunodiffusion techniques indicated that the antiserum contained antibodies to proteins other than lipoprotein lipase (bovine milk and serum proteins) and that these antibodies could be eliminated by adsorption with bovine serum and a beta-casein preparation.

Adsorption↗
PubMed1980

[Lipoprotein-lipase-activity in human milk (author's transl)].

Lipoprotein-lipase-activity has been determined in human milk between the 3rd and the 10th post-partum days in women from different ethnic origins. This activity is low in the colostrum, it increases at the 4th and 5th days and remains stable between the 6th and the 10th day. There are important variations of the LPL-activity from one woman to another. Two variation-factors have been noticed. The first is an ethnic factor. It is apparent event if the diet is exactly the same in all women. In the milk, indeed, the activity of French women is much lower. It is about three times less than the activity of Yugoslavian of African women. The second is the galactogenic powder that has been estimated by the natural duration of lactation. We can see that the activity of women, who have to stop breast-feeding because of insufficient milk, is lower than the activity of women who can decide how long they will breast-feed their child. We took as a hypothesis that the milk is a means of elimination for the mammary-LPL. This enzyme is supposed to have done first its physiological action at the surface of mammary glandular cells. Ours results show more facts in favor of this hypothesis.

Adult↗
PubMed1979

[A simple micromethod for sphingomyelinase determination (author's transl)].

A rapid and sensitive micromethod for routine determination of sphingomyelinase activity of leukocytes, fibroblasts and hair roots is described. This method makes use of the natural radioactive substrate of the enzyme. The product of the reaction is isolated by direct application of the incubation mixture on silica gel plates followed by ascending chromatography. The sensitivity of the method allows sphingomyelinase determination in less than 0.5 microgram of fibroblast proteins.

Carbon Radioisotopes↗
PubMed1979

Phospholipase activities in subcellular fractions of human platelets.

A homogenate of human platelets was fractionated by zonal ultracentrifugation into membranes, various granules and mitochondria. The membrane fraction was composed of two populations. The first, which represented 75% of the proteins, was rich in plasma membranes; the second, which represented the remaining 25%, was rich in microsomal membranes. Lysophospholipase was essentially localised in the cytosol. Phospholipase A1 which was only weakly bound to membranes, was mostly found in the soluble fraction (75%); the remainder was located in the plasma membranes and the mitochondria. Two-thirds of the phospholipase A2 was found in the particulate fractions.

Adult↗
PubMed1979

[Phospholipase A2 activity in rat platelets].

Rat blood platelets show phospholipase A2 activities twenty times higher than human platelets. The breakdown of PE at pH 7.2 is linear for 15 minutes. There is no degradation at pH less than 5; the maximal activity is in the pH range 5.5-7.5. The presence of Ca2+ increases the phospholipase activity; an excess is not inhibitory. The optimal activity is obtained with 16 microM substrate concentration. Substrate inhibition is observed when the concentration exceeds 25 microM.

Animals↗