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Biomedical subjects

P Louisot

Publications and source records attributed to P Louisot.

At least 163 records · Page 9Linked to original sources
PubMed1983

Effect of phospholipids on the regulation of a soluble galactosyltransferase in aortic wall.

A galactosyltransferase activity is located in the cell-sap of aortic intima-media cells. This enzymatic system calatyzes [14C]galactose transfer from UDP-[14C]galactose into endogenous and exogenous proteinic acceptors. Labelled products are isolated from the proteinic fraction obtained in 20% trichloroacetic acid pellet or from organic solvent extractions. Maximal [14C]galactose incorporation occurs at pH 7.8 in Tris-HCl buffer in the presence of 0.1 mM MnCl2 at 30 degrees C. The enzymatic activity is modified by phospholipids, particularly by phosphatidic acid and lysophosphatidylcholine, which behave as mixed inhibitors, while L-alpha-phosphatidylserine interacts as a competitive inhibitor. The effect of phospholipids is not stereospecific but appeared to be closely related to their polar headgroups, especially the acidic headgroups of phosphatidylcholine and phosphatidic acid. The chain length and the unsaturation degree of fatty acids involved in phospholipid structures are not a main factor of regulation. The lysophosphatidylcholine effect could be explained by its solubilization properties, as non-ionic detergents interact in the same way with galactosyltransferase activity. Exogenous phospholipids probably interact with the enzymatic environment by their own molecular arrangement and so could exert a control on galactosyltransferase activity or lead to a conformation change of this enzyme.

Aorta↗
PubMed1983

Enzymatic screening of human uterine cervical biopsies in nonpregnant and pregnant women at parturition.

Twelve enzymatic activities, involved in the metabolism of proteins, collagen, glycosaminoglycans, or in the energy metabolism, were studied in 72 cervical biopsies obtained after delivery of the placenta and in 12 cervices obtained by hysterectomy in nonpregnant patients. Although these activities display high interindividual variations, they are greatly and significantly increased at parturition as compared to the nonpregnant state, with the exception of creatine kinase, which is maximum in cervices obtained from nulliparous nonpregnant women. The activities are low in the group of women who are 35 to 40 years old. The other studied factors (blood group, parity, pregnancy duration, labor length, treatment, state of the cervix at the 9-month examination) have no clear influence on the enzymatic levels. The results are discussed in relation to the well-known structural changes of the cervix at parturition.

Adult↗
PubMed1983

Macromolecular, histological, ultrastructural and immunocytochemical characteristics of the neointima developed within PTFE vascular grafts. Experimental study in dogs.

The nature and characteristics of the tissue that develops on the inner surfaces of vascular arterial PTFE prostheses have been investigated by histological, morphometrical, ultrastructural, and immunocytochemical criteria. The ability of this tissue to synthetize glycoproteins and glycosamino-glycuronoglycans (previously called mucopolysaccharides) has been compared to that of the normal arterial wall. PTFE prostheses were used for carotid replacement in the dog and studied until the 90th postoperative day. These prostheses were mainly characterized by (1) a limited or even absent neointimal tissue proliferation; (2) the absence of an endothelial-like structure on the prosthesis using scanning electron microscopy and immunocytochemical staining with rabbit antidog factor VIII-related antigen sera; (3) limited activities of both microsomial enzymes (sialyl transferase and N-acetyl-glucosaminyl-transferase) but marked xylosyl transferase activity; and (4) inverse qualitative distribution of the glycosaminoglycans, i.e., decrease of heparan sulfate and chondroitin-6-sulfate and increase of hyaluronic acid and dermatan sulfate. The absence of morphological evidence of an endothelial structure at the blood--prosthesis interface even 3 months after implantation and the marked functional impairment in the biosynthesis of macromolecular components responsible for the normal blood--vessel interface suggest that this newly developed tissue cannot be considered a true vascular endothelium.

Animals↗
PubMed1983

Effect of phospholipids on membrane-bound and solubilized mannosyltransferase activity from aortic wall.

Phospholipids interact on the membrane-bound and solubilized mannosyltransferase activity. The biosynthesis of Dol-P-Man is strongly inhibited by phosphatidic acid and lysophosphatidylcholine. The effect of phospholipids is not related to stereospecificity. Chemical properties of phospholipids (ester or ether bond, length of fatty acids and polarity of head groups) are not an essential factor for inhibition. The different parameters involved in enzymatic reaction of glycosylation are not modified by phospholipids, in particular the integrity of GDP-[14C]mannose. The inhibitory effect of lysophosphatidylcholine and phosphatidic acid on mannosyltransferase activities is related to their possible formation of micellar structures which definitely induce a conformation change of this enzyme.

Animals↗
PubMed1983

Biochemical evidence for the role of alkyl-lysophospholipids on liver sialyltransferase.

Antineoplastic alkyl-lysophospholipids were found to exert a strong inhibitory effect on membranous or solubilized asialomucin-sialyltransferase (CMP-N-acetylneuraminate: D-galactosyl-glycoprotein N-acetylneuraminyltransferase, EC 2.4.99.1) activity. This inhibitory effect was dependent on the presence of the choline moiety in position 3 of the glycerol molecule, as well as on the presence of long ether-linked aliphatic side chain in position 1 and the absence of any large substituent in position 2. As an example, 1-octadecyl-2-O-methyl-glycero-3-phosphorylcholine acted as a mixed-type inhibitor. Such an inhibitory process on sialyltransferase activity might be an additional factor in the tumor cell destructive effect of alkyl-lysophospholipids.

Animals↗
PubMed1983

Biosynthesis of pulmonary glycoconjugates--V. Biosynthesis of oligosaccharide inner core region of N-glycoprotein in lung microsomes.

Lung microsomes are able to synthesize dolichyl-mannosyl-phosphate, which stimulates the biosynthesis of a product (P1), soluble in chloroform/methanol/water (10:10:3, v/v). In presence of pulmonary dolichyl-mannosyl-phosphate, liver microsomes synthesized 3 mannosylated products: X1 product recovered in chloroform/methanol extract, X2 and X3 products soluble in chloroform/methanol/water (10:10:3, v/v). Mild acid hydrolysis of P1 product released one mannosylated oligosaccharide which remained at the origin in our solvent system, since two mannosylated oligosaccharides, released from products synthesized in liver, moved very slowly. Addition of N,N'-diacetyl [14C]chitobiosyl-pyrophosphoryl-dolichol to lung microsomes incubated with GDP-[3H]mannose stimulated the synthesis of a [3H, 14C]product extracted with chloroform/methanol (2:1, v/v). Mild acid hydrolysis of this product released [3H, 14C]oligosaccharide which moved very slowly on paper chromatography, in our solvent system. These results demonstrate that lung tissue can synthesize the oligosaccharide inner core region of N-glycoprotein with the sequence (Man)x-(GlcNac)2. But pulmonary dolichol pool is probably involved in other lipid biosynthesis pathways.

Animals↗
PubMed1983

Chromatofocusing of purified placental sphingomyelinase.

To establish the profile of the multiple forms of placental lysosomal sphingomyelinase, we have developed in a preliminary step, a new sequence of purification. This protocol has a good yield such that the final preparation is representative of the whole enzyme. Using chromatofocusing, purified sphingomyelinase is resolved into 4 major forms whose pI's are 7.2, 6.5, 5.9 and 5.2. Chromatofocusing is preferable to isoelectric focusing because it is more rapid, more reproducible and above all it provides a constant profile of activity which is not influenced by experimental conditions, in particular, detergent concentration.

Chromatography↗
PubMed1983

[Demonstration of a double subcellular localization of cerebral fucosyltransferase].

We have shown that the fucosyltransferase activity was located in two subcellular fractions: the microsomes and the synaptosomes. The localization of enzyme activity was identical in the young and in the adult rat brain. The values of some parameters of the microsomal enzyme (Km, optimum temperature, optimum pH) in the young and in the adult rat brain shown that the enzyme affinity for its substrate is in relation with the brain maturation.

Aging↗
PubMed1983

[Iodized contrast media. I. effector action on serum enzymes].

In vitro studies were done to examine the effects of contrast media on blood enzymatic activities. The results observed are very significant: in the most simple cases they result in a competitive or mixed-type type inhibition of these enzymes. In systems which involve two substrates and two products a Bi-Bi ping-pong enzymatic mechanism is transformed in Bi-Bi random enzymatic mechanism.

Contrast Media↗
PubMed1982

Impaired glycosylation in liver microsomes of orotic-acid-fed rats.

In rats fed orotic acid, the incorporation in liver subcellular fractions of sugars injected intraperitonealy is altered only for mannose, but not for fucose or galactose. Direct determinations of several glycosyltransferases are done in smooth and rough microsomes: fucosyl-, glactosyl-, N-acetylglucosaminyltransferase activities are at quite similar levels in normal and fatty livers. By contrast, sialyltransferase activity is increased (+50%) in smooth microsomes of fatty livers, while mannosyltransferase activity is inhibited by 30%. These alterations are not caused by interfering reactions (pyrophosphatases or proteases). For the mannosyltransferase activity, the inhibition is found in the dolichylphosphorylmannose intermediates. Kinetic studies suggest that there is deficiency of both enzyme and endogenous dolichyl phosphate.

Animals↗
PubMed1982

Effects of 1-palmitoyl-sn-glycero-3-phosphorylcholine on the properties of a solubilized sialyltransferase activity from mouse liver.

Asialomucin-sialyltransferase (CMP-N-acetylneuraminate:D-galactosyl-glycoprotein N-acetylneuraminyltransferase, EC 2.4.99.1) activity was solubilized from mouse liver microsomes by sonication. The catalytic activity was markedly inhibited by a series of lysophosphatidylcholines, particularly 1-palmitoyl-sn-glycero-3-phosphorylcholine. This lysophospholipid did not alter optimal conditions for enzyme activity. In contrast, it was found that affinities for binding of Mn2+, desialylated mucin and CMP-sialic acid were decreased by adding the lipid. A reasonable interpretation of these data is that the presence of phospholipid modifies the enzyme conformation.

Animals↗
PubMed1982

Effects of defined synthetic phospholipids on glycosylation processes. Modifications of membrane-bound N-acetylglucosaminyl-transferase and solubilized sialyl-transferase activities.

In this paper, we study effects of phosphatidylcholine synthetic derivatives on two different glycosyltransferasic systems, a membranous mitochondrial N-acetylglucosaminyl-transferase and a solubilized microsomal sialyl-transferase. From all our results, we proved the strong inhibitory effect of lysophosphatidylcholines in these glycosylation processes. We investigated then the relationship between this inhibitory effect and the chemical structure of the studied phospholipids. From this work, it became obvious that the most important inhibitory effect is obtained with a molecule containing a long aliphatic side chain in sn-1 of glycerol, a carbon atom devoid of any large group in sn-2 and an hydrophilic part in sn-3 (specially choline).

Animals↗
PubMed1982

Characterization of a mannosyl-lipid compound of microsomal fractions of rat pancreas and influence of diet.

1. High-starch diet induces an activation of rat pancreatic microsomal mannosyl-transferase activity as compared with a standard diet or a high-fat diet. 2. This increase is found in a mannose-containing lipid which is identified as a dolichyl-phosphoryl-mannose on the criteria of DEAE-cellulose chromatography, alkaline and acid hydrolysis, thin-layer chromatography and identity of this endogenous product with the [14C]mannose-containing product synthesized in presence of exogenous dolichyl-monophosphate added to the incubation medium. 3. Kinetic parameters (Km and Vmax) of the enzyme versus polyprenic acceptor are not modified by the diet. 4. The results indicate that the activation of the mannose transfer is principally due to an increase of the polyprenic endogenous acceptor by the high-starch diet.

Animals↗
PubMed1982

[Biosynthesis of pulmonary glycoconjugates. Mechanism of glucosylation of protein and lipid acceptors].

In sheep lung microsomes, we have shown that glucosyl-transferases catalize the transfer of glucose from UDP-glucose into four different acceptors. The glucosylated products obtained are as follows: - a glucosyl-phosphoryl-polyprenol (product A) extractable by chloroform/methanol (2:1 by volume). - a product B extractable by chloroform/methanol/water (10:10:3 by volume). The product B was a mixture of five glycolipids, one of them having a chromatographic behaviour similar to the behaviour of a tetrahexosylceramide (asia-lo-GM1). - a product C insoluble in water and organic solvents which has been demonstrated to be a glycoproteinic compound. The molecular weight of this product C was 160 000 as estimated by gel-filtration. The carbohydrate moiety is composed of small oligosaccharides which are found to be attached by O-glycosidic bond to the protein chain. This linkage is not a collagen-like bond.

Animals↗
PubMed1982

Substrate specificity of cerebral GDP-fucose: glycoprotein fucosyltransferase.

Solubilized sheep brain fucosyltransferase was shown to transfer fucose from GDP-fucose onto glycoprotein and glycopeptide acceptors, such as asialofetuin, asialotransferrin, their glycopeptides and glycopeptides from ovalbumin, but not on to monosaccharides and disaccharides such as galactose, N-acetylglucosamine and lactose. Competition studies between asialofetuin and glycopeptide V from ovalbumin provided evidence that both substrates compete for a common enzyme active site. The position of the fucosyl linkage was then investigated. Endo-beta-N-glucosaminidase D digestion of fucosylated and acetylated glycopeptide V showed that fucose is not linked to asparagine-linked N-acetylglucosamine. Hydrazinolysis and nitrous acid deamination performed on asialofetuin and glycopeptide V proved that fucose is not linked to external galactose or N-acetylglucosamine either. Thus we assume that fucose is linked to the oligomannochitobiosyl core of the glycan, and probably to the second N-acetylglucosamine.

Acetylglucosaminidase↗