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Biomedical subjects

J Polonovski

Publications and source records attributed to J Polonovski.

At least 19 recordsLinked to original sources
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↗
PubMed1979

Diagnosis of Niemann-Pick disease by analysis of hair-roots.

A micromethod for the measurement of sphingomyelinase in hair root lysates was described. With this method, 22 normal individuals, 3 children affected with Niemann-Pick disease and 2 carriers have been studied. It seems clear that Niemann-Pick homozygotes can be diagnosed definitively, but more extensive studies arenecessary to decide if carrier detection with hair-roots is possible. The particular interest of using hair roots is that the material can be sampled easily and mailed without special precautions.

Clinical Enzyme Tests↗
PubMed1979

Effect of concanavalin A on lysosomal enzyme content of Hela cells.

Precoating Hela cells with concanavalin A (Con A) induces a decrease of lysosomal enzyme intracellular content, and correlatively increases the amount of these enzymes in the culture medium. Possible mechanisms of the lectin effect are discussed in relation to the hypothesis of the secretion-endocytosis cycle of lysosomal enzymes.

Concanavalin A↗
PubMed1978

Affinity chromatography on heparin-sepharose of rat adipose tissue triglyceride lipase from cytosol.

Subfractionation of the fat free homogenate of rat adipose tissue showed that a high yield of triglyceride lipase was recovered reproducibly in the microsomal supernatant fraction (cytosol) when rat epididymal fat pads were homogenized in sucrose-EDTA-Tris medium. Triglyceride lipase was bound on heparin-Sepharose. Hydrolyzing activity towards triacylglycerol was eluted as a single, sharp peak in 0.7 M NaCl, 5 mM sodium barbital and 20% glycerol (pH 7.0). The triglyceride lipase was not inhibited by 1 M NaCl and not stimulated by the presence of fresh human serum. A lipoprotein-lipase activity was demonstrable in the cytosol when adipose tissue from fed rats were used. Fasting of the animals lowered this activity.

Adipose Tissue↗
PubMed1978

Phospholipases of plasmic membranes of adipose tissue. Possible intermediaries for insulin action.

In the present investigation we have shown that cytoplasmic membranes of adipocytes contain A1 and A2 phospholipase activities which are optimal in a buffer with 5 mM Ca2+ (pH 8.5). Insulin enhances these activities within phosphatidylethanolamine. Insulin increases also the amount of free fatty acids in membranes. Rodbell and Blecher have already shown an insulin-like action of phospholipases towards the uptake of glucose and amino-acids by adipocytes. Shier and Asakawa have recently described that lysolecithin and unsaturated fatty acids can change nucleotide-cyclase activities of cytoplasmic membranes towards GTP and ATP; lysolecithins and Triton X 100 seem to react in an identical way. Results from these studies give new suggestions on insulin action; phospholipase activation changes membrane physiochemical properties inducing an increase of glucose carrier mobility and leading the membrane cyclase enzyme (s) towards GMP cyclic synthesis.

Adipose Tissue↗
PubMed1978

[A new protein from human plasma lipoproteins: isolation and partial characterization of apolipoprotein G].

A new apolipoprotein has been identified in VHDL1 and in HDL. This protein is immunologically distinct from already isolated apoproteins. It was isolated by column chromatography on hydroxylapatite. In polyacrylamide gel electrophoresis, its mobility is very close to that of apo D. The amino acid composition differs from those of the well characterized polypeptides of the human plasma lipoproteins. It contains glucosamine. The apparent molecular weight is 72 000 +/- 2 000 in the presence and absence of reducing agent. According to the ABCDEF nomenclature, this protein can be named apolipoprotein G (apo G). It is present in a lipoprotein distinct from the lipoproteins A and D among the VHDL1 : this new lipoprotein can be named lipoprotein G (LPG).

Amino Acids↗
PubMed1978

Abnormal lipoproteins in a case of primary biliary cirrhosis.

The serum of a patient diagnosed as a primary biliary cirrhosis was studied during the various evolutive stages of the disease. During the non-icteric period, the serum lipoprotein had the chemical composition (rich in cholesterol and phospholipids) of that found in cholestasis; however the bilirubinemia was normal, and no LPX was detected; there was a normal esterified to total cholesterol ratio and the alphaLP had not decreased, as expected, but increased and was divided into two fractions; immunoelectrophoretic studies of ultracentrifugal fractions showed some LP with HDL immunological properties, but with lower densities than that of normal HDL. We suggest that the phospholipid overloading of some of these HDL in the patient's serum could explain the changes in density. Some months after this study, the patient's serum exhibited the characteristics found in cholestasis, with disappearance of HDL and appearance of LPX. During the subsequent period, the serum again contained phospholipid rich HDL and LPX. In fact several LPX with different densities were found. It seems, therefore, that in cholestasis, LP undergo modification in which the HDL peptide chains play an important role.

Bilirubin↗
PubMed1978

Turnover of phospholipid linoleic and arachidonic acids in human platelets from plasma lecithins.

Incubation of platelet-rich plasma with high density lipoproteins labeled either with 1-acyl-2[1-14c]-arachidonoyl-sn-glycero-3-phosphocholine or 1-acyl-2-[1-14c]linoleoyl-sn-glycero-3-phosphocholine showed the existence of a pool of phosphatidylcholine in platelets, which rapidly exchanges with the phosphatidylcholine in plasma. The labeled linoleic and arachidonic acids from the respective labeled phosphatidylcholines were found in the other glycerophospholipids. These transacylation processes were much more active with the arachidonoyl-labeled phosphatidylcholine than with linoleoyl-labeled phosphatidylcholine. Arachidonic acid was mainly found in the phosphatidylinositol.

Arachidonic Acids↗
PubMed1978

A rapid method for lecithin:cholesterol acyltransferase estimation in human serum.

All the described procedures for lecithin:cholesterol acyltransferase (LCAT) determination in the plasma have raised criticisms: Lack of sensitivity for methods using colorimetric determination of unesterified cholesterol or phosphatidyl-choline in plasma before and after incubation at 37 degrees C. Incomplete isotopic equilibrium of the free cholesterol substrate between the different lipoproteins in radioassay procedures. Gas-liquid chromatography methods cannot be used when LCAT activity is low. A new method, easier, more sensitive and accurate has been developed in our laboratory:plasma samples are delipoproteinized by coprecipitation with Intralipid, dextran sulphate, and calcium chloride. Cholesterol esterification is assayed by a short incubation (30 min) of 100 microliter delipoproteinized plasma and a 30 microliter of 3H-cholesterol-labelled substrate. About 15% of cholesterol is esterified in these conditions in 30 min (35 +/- 7 micromole/h/l). The LCAT reaction is linear for about one hour.

Calcium Chloride↗
PubMed1977

[Platelets fatty acid variation in patients with atherosclerosis (author's transl)].

Plasma linoleic acid levels were found to be low in the atherosclerosis patients investigated. In contrast, platelet arachidonic acid levels were decreased only when atherosclerosis was combined with diabetes or mixed hyperlipidemia. In acute vascular thrombosis, a marked decrease in platelet arachidonic levels occurrrd, irrespective of whether the patient had atherosclerosis or not.

Arachidonic Acids↗