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J Frot-Coutaz

Publications and source records attributed to J Frot-Coutaz.

At least 19 recordsLinked to original sources
PubMed1999

The prolyl aminopeptidase from Lactobacillus delbrueckii subsp. bulgaricus belongs to the alpha/beta hydrolase fold family.

Prolyl aminopeptidase (PepIP) of Lactobacillus delbrueckii subsp. bulgaricus displays the Gly-x-Ser-x-Gly-Gly consensus motif surrounding the catalytic serine of the prolyl oligopeptidases family. Sequence comparison revealed that this motif and two other domains appear well conserved among bacterial PepIPs and members of the alpha/beta hydrolase fold family. Secondary structural predictions of PepIP were performed from amino acid sequence and corroborated by circular dichroism analysis. These predictions well matched the core structure of alpha/beta hydrolases organised in eight beta-sheets connected by alpha-helices. We obtained 26 mutants of PepIP by chemical or site-directed mutagenesis. Most substitutions associated with stable and inactive mutant proteins were mainly located in the three conserved boxes (including the catalytic serine motif). Taken together, our results strongly suggest that PepIP belongs to the alpha/beta hydrolase fold family and that Ser107, Asp246 and His273 constitute the catalytic triad of the enzyme.

Amino Acid Sequence↗
PubMed1992

Aspergillus niger G proteins: subcellular localization.

Aspergillus niger postmitochondrial fraction, which contains high GTPase activity and high GTP binding capacity, has been subjected to subcellular fractionation on a sucrose gradient. A cytosolic and four membranous populations have been separated according to their relative density. The main difficulty has been the characterization of the plasma membrane of the fungus. This fraction, which does not contain any typical enzyme, has been identified after iodination of the outer proteins of protoplasts from A. niger. The immunological detection has shown the occurrence of cytosolic G proteins and membranous small G proteins located not only in the plasma membrane but also in the membranes of the endoplasmic reticulum.

Aspergillus niger↗
PubMed1992

In vitro transfer of N,N'-diacetylchitobiose to glycoproteins in rat liver nuclei.

This work demonstrates that (N-acetyl[14C]glucosamine)2 is transferred from dolichyl pyrophosphate-(N-acetyl[14C]glucosamine)2 to endogenous nuclear glycoproteins. The (N-acetyl[14C]glucosamine)2 moiety is N-linked, since it can be released from the tryptic glycopeptides by N-glycosidase F and by hydrazinolysis, but not by beta-elimination. The biological significance of this direct transfer of N,N'-diacetylchitobiose to nuclear proteins remains to be elucidated.

Animals↗
PubMed1992

In vitro transfer of N-acetylglucosamine to endogenous glycoprotein acceptors catalyzed by the nucleus and the cytoplasmic membranes prepared from L1210 cells.

The non-nuclear membranes and the nuclei prepared from L1210 cells catalyze the in vitro transfer of N-acetyl(14C)glucosamine from UDP-N-acetyl(14C)glucosamine to endogenous glycoprotein acceptors. Adequate analysis of these acceptors have demonstrated that the nucleus has its own N-acetylglucosaminyltransferase system that leads to the formation of N-N'-diacetylchitobiosylated proteins.

Acetylglucosamine↗
PubMed1991

Characteristics of N-acetylglucosamine transfer to nuclear acceptors of rat hepatocytes.

In this report, we describe the main characteristics of the transfer of N-acetylglucosamine within the nucleus of rat hepatocytes. The glycosylation pathway includes the presence of lipids which mediate the nuclear proteins glycosylation. The level of dolichylphosphate seems low and thus could be a regulation factor in the nuclear glycosylations. The discussion deals with the membranous character of the acceptors and the N-acetylglucosaminyltransferase, the N-linkage of the sugar moiety to nuclear proteins and the function of such glycosylation.

Acetylglucosamine↗
PubMed1990

Effect of vitamin A deficiency on the in vitro transfer of mannose and N-acetylglucosamine in rat liver nuclei.

Liver nuclei, prepared from normal and vitamin A-deficient rats, were incubated in the presence of GDP-(14C)mannose or UDP-N-acetyl(14C)glucosamine and the labelled glycoproteins analysed by SDS PAGE. Fluorographic analysis has shown that (14C) mannose labelling is enhanced by vitamin A deficiency whereas N-acetyl(14C)glucosamine transfer remains approximately at the same level regardless of the vitamin A status; we did not notice any modification when the proteins were monitored by Coomassie blue or by silver nitrate.

Acetylglucosamine↗
PubMed1989

Influence of vitamin A status and DDT on vitamin A-dependent protein mannosylation in rat liver.

Male Wistar rats of different vitamin A status (total depletion to moderate deficiency) were administered DDT (5 mg/kg/day) or vehicule (corn oil) i.p. daily for 14 days. Vitamin A-dependent protein mannosylation was measured either by in vivo incorporation of [3H]mannose into liver glycoprotein or by in vitro assay of incorporation of [14C]mannose into mannosylretinyl phosphate. Vitamin A deficiency resulted in a significantly impaired in vivo incorporation of mannose in liver glycoprotein but had no effect on the in vitro transport of mannose via retinyl phosphate. Although DDT induced an increase synthesis of liver proteins in smooth endoplasmic reticulum and caused a diminution of the hepatic vitamin A content, it did not affect vitamin A-dependent protein mannosylation.

Animals↗
PubMed1988

Protein-mediated fusion of liposomes with microsomal membranes of Aspergillus niger: evidence for a complex mechanism dealing with membranous and cytosolic fusogenic proteins.

Membrane fusion is a fundamental and wide-spread phenomenon in the functioning of cells. Many studies were carried out concerning fusion of plasma membranes as for example cell-cell fusions or uptake by cells of lipid-enveloped viruses. The present study deals with the interaction of intracellular membranes of Aspergillus niger with artificial membranes (liposomes). Association is monitored by the uptake of radioactive liposomes by fungal microsomal membranes. The discrimination between aggregation and pure fusion is done by layering the liposomes-microsomes mixture on a continuous sucrose gradient. The accurate quantitation of the fusion phenomenon is monitored with a fluorescent assay based on resonance energy transfer (Struck, D.K. et al. (1981) Biochemistry 20, 4093-4099). Both methods show that, at physiological pH, there is a spontaneous fusion of microsomes with cholesterol-free liposomes. This phenomenon is protein dependent as trypsinized microsomal membranes are no longer able to fuse with liposomes. Biological significance of the fusion process has been demonstrated using microsomal intrinsic protein mannosylation assay; the enhancement of the lipid to protein ratio due to the fusion of liposomes with microsomes of A. niger results in an increase in the rate of endogenous proteins mannosylation. Moreover, cytosolic proteins of A. niger promote the fusion of any kind of liposomes with microsomes.

Aspergillus niger↗
PubMed1988

Presence of a cellular retinylphosphate binding protein in rat liver.

A retinylphosphate binding activity, resolved during purification, has been discovered in rat liver cytosol. The partial purification includes ammonium sulfate precipitation and DEAE-cellulose chromatography. The macromolecular component responsible for the binding has a sedimentation coefficient of about 2 S and is sensitive to pronase. This binding is reversible and specific for retinylphosphate, since retinol, retinoic acid and retinoylphosphate do not compete with [3H]retinylphosphate.

Animals↗
PubMed1988

Glycoprotein mannosylation in rat liver nuclei.

Nuclei and non-nuclear membranes were tested for their ability to transfer in vitro (14C)mannose from GDP-(14C)mannose to endogenous glycoprotein acceptors in the presence and in the absence of exogenous retinyl-phosphate. Electrophoretic analysis shows that retinylphosphate is responsible for the labeling of a few endogenous acceptors only in the non-nuclear membranes; in the nuclei the mannosylation reaction is not retinylphosphate dependent and the electrophoretic profile of the labeled protein acceptors is different from that of the non-nuclear membranes.

Animals↗
PubMed1988

Transfer of N-acetylglucosamine to endogenous glycoproteins in the nucleus and in non-nuclear membranes of rat hepatocytes: electrophoretic analysis of the endogenous acceptors.

The transfer of N-acetyl(14C)glucosamine from UDP-N-acetyl(14C)glucosamine to endogenous glycoproteins acceptors were studied comparatively in the nuclei and in the non-nuclear membranes of rat hepatocytes. Electrophoretic and autoradiographic analysis show that most of the glycoprotein acceptors of the nuclei differ from those of the non-nuclear membranes in terms of molecular weight. In addition, it may interesting to mention that in the nuclear fraction a 30% inhibition by tunicamycin is obtained for concentrations as low as 0.03 microM, whereas at this concentration no effect is detected in the non-nuclear membranes. In the presence of 0.2 microM tunicamycin, the inhibition does not go beyond 25% in the latter fraction but goes up to 80% in the former. The previous results demonstrate clearly that a particular glycosylation reaction occurs in the nucleus.

Acetylglucosamine↗
PubMed1987

Vitamin K1 binding protein in milk.

Cow's milk has been shown to contain a protein complex which is able to bind vitamin K1 in a reversible manner. This binding property has been investigated by the celite method which consists in creating a dynamic equilibrium between the adsorbent, the celite and the protein complex for the ligand (vitamin K1). Based on competition experiment, the binding is specific and the vitamin K1 binding protein complex has a molecular weight equal to or higher than 7.5 X 10(2) KD.

Animals↗
PubMed1985

Spatial aspects of mannosyl phosphoryl retinol formation.

Rat liver microsomes catalyze the transfer of mannose from GDPmannose to both retinyl phosphate and dolichyl phosphate to form mannosylphosphorylretinol, mannosylphosphoryldolichol and GDP. The two reactions differ in term of reversibility. In fact, a 200-fold isotopic dilution of GDP[14C]mannose by unlabeled GDPmannose causes mannosylphosphoryldolichol labeling to disappear almost completely, while mannosylphosphorylretinol labeling remains at the same level. The same observation can be made if the mannose donor is removed by centrifugation and replaced by excess GDP; again mannosylphosphorylretinol is stable, but mannosylphosphoryldolichol drops down to one-third of its initial level, as expected for, respectively, a non-reversible and a reversible reaction. Placed in an aqueous medium, mannosylphosphorylretinol releases mannose 1-phosphate (beta configuration) whereas it is quite stable when kept in a membranous environment. These results strongly suggest that mannosylphosphorylretinol as soon as it is formed is segregated in such a way that it is no longer available to the back-reaction; the functional consequence of this segregation would be the possibility for mannosylphosphorylretinol to mannosylate some non-polar regions of certain protein chains.

Animals↗
PubMed1982

Aspergillus niger van Tieghem mannosylation: polyprenylphosphate mannosyltransferase specificity.

Aspergillus niger van Tieghem microsomes contain an enzyme that catalyzes mannose transfer from GDP-mannose to polyprenylphosphate. The studies of the specificity of this enzyme for both the sugar donor (nucleoside diphosphate sugar) and the acceptor (polyprenylphosphates that were made available to the enzyme by means of the fusion of acceptor-loaded liposomes with the microsomal membranes) gave the following results. i) All the polyprenylphosphates from C15 to C120 were acceptors except retinylphosphate. ii) The specificity of the enzyme for both the sugar and the base is very strict.

Aspergillus niger↗
PubMed1979

Evidence for glycosyltransferases in trout liver microsomes (Salmo gairdneri).

1. Trout (Salmo gairdneri) serum is rich in glycoproteins which are synthetized in liver. 2. An attempt to localize glycosyltransferases in hepatocytes is described, using cellular fractionation and marker enzyme determination. 3. Galactosyltransferase, mannosyltransferase, N-acetyl-glucosaminyl transferase, glucosyltransferase, sialyltransferase (on exogenous acceptor) are found in a microsomal fraction obtained by centrifugation at 117 X 10(5) g min of the post-mitochondrial supernatant. 4. Mannose is transferred to endogenous lipids and proteins.

Animals↗
PubMed1975

[Molecular weight of a membrane receptor of UDP-glucose].

Rat liver microsomal membranes have been shown to contain an UDP-glucose binding protein. Its mol. wt was estimated to be 120 000 by gel filtration and by ultracentrifugation in a sucrose gradient. The receptor activity was purified by gel filtration on Sephadex G200 and analysed by gel-electrofocusing.

Binding Sites↗