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M B Martel

Publications and source records attributed to M B Martel.

16 recordsLinked to original sources
PubMed2002

Purification and characterization of a glucoamylase secreted by the plant pathogen Scierotinia sclerotiorum.

Among the lytic enzymes secreted by the phytopathogen fungus Sclerotinia sclerotiorum, a starch-degrading enzyme has been isolated and characterized. This glycoprotein of 72 kDa is composed of several isoforms ranging from pI 4.8 to 5.4. The enzymatic parameters have been determined. Specificity studies together with the analysis of the reaction products show that it is an alpha-1,4-glucanohydrolase. This result is also corroborated by the analysis of the N-terminal and two inner amino acids sequences that are very similar to fungal glucoamylase genes or enzymes so far sequenced.

Amino Acid Sequence↗
PubMed1998

Purification and characterization of two endopolygalacturonases secreted during the early stages of the saprophytic growth of Sclerotinia sclerotiorum.

Two endopolygalacturonases (endo-PGs) secreted at the early stage of cultures of Sclerotinia sclerotiorum grown on polygalacturonate medium, were purified to apparent homogeneity, using ion exchange chromatography. They are glycoproteins of an apparent weight of 42 and 41.5 kDa and a pI of 4.8. The two purified isoforms found in early cultures were not detected in late cultures. Purification of the isoforms secreted at different stages of growth revealed that the increase of polygalacturonase activity during the culture corresponds to a sequential production of enzymes and to the successive replacement of isoforms by new enzymes.

Ascomycota↗
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↗
PubMed1990

Solubilization of UDPglucose-ceramide glucosyltransferase from the Golgi apparatus.

The choice of a suitable detergent for solubilization of UDPglucose-ceramide glucosyltransferase from Golgi membranes has been investigated. Among the various classes of detergent, CHAPS, a zwitterionic detergent, was used as it produced a substantial activation of the enzyme activity. 30% of the enzyme activity and 50% of proteins were solubilized in the first attempts. Further experiments were conducted with addition of a second detergent, Zwittergent 3-14 which increased enzyme recovery to 45%. Lastly, reducing the concentrations of buffer and divalent cations Mn2+, Mg2+ and introducing glycerol (20%, v/v) allowed 80% of proteins to be solubilized together with 68% of the ceramide glucosyltransferase activity.

Animals↗
PubMed1990

Effect of phospholipids on UDP-glucose: ceramide glucosyltransferase from Golgi membranes.

1. The removal of phospholipids completely abolished the activity of the enzyme UDP-glucose:ceramide glucosyltransferase from Golgi membranes. 2. Modulation of enzyme activity by phospholipids was undertaken on the solubilized form of the enzyme. 3. Well-defined fatty acyl chains and polar head groups were necessary for maximal stimulation by phospholipids. 4. A specific requirement for phosphatidylcholine is suggested by preliminary experiments of reconstitution of enzyme activity with phosphatidylcholine vesicles.

Animals↗
PubMed1986

Topology of glucosylceramide synthesis in Golgi membranes from porcine submaxillary glands.

The topology of ceramide glucosyltransferase and de novo synthesized glucosylceramide was studied in sealed and 'right-side-out' vesicles of porcine submaxillary glands derived from Golgi apparatus. Pronase treatment which did not cause any breakdown of the luminal glycoprotein galactosyltransferase activity, inhibited the ceramide glucosyltransferase to more than 50% at a ratio proteinase to Golgi protein 1:100. Trypsin at the same concentration, while producing no inactivation of luminal galactosyltransferase, caused a complete loss of ceramide glucosyltransferase activity. The membrane-impermeable compound, DIDS, which did not cause any inhibition of the galactosyltransferase, inhibited the ceramide glucosyltransferase (70% reduction at 80 microM DIDS). Thus, the enzyme ceramide glucosyltransferase is accessible from the cytoplasmic side of the Golgi vesicles. The orientation of the newly synthesized glucosylceramide is studied by the ability of the enzyme glucosylceramidase to hydrolyse this compound both on intact and on disrupted vesicles. The same percentage (respectively, 36 and 30%) of hydrolysis was obtained during an incubation of 3 h, showing that glucosylceramide is not at all protected from external hydrolysis. Pronase-treated vesicles revealed an increase in glucosylceramidase hydrolysis (up to 45%), which indicates that glucosylceramide that glucosylceramide may be cryptic. All these results indicate that the ceramide glucosyltransferase, as well as related glucosylceramide, are cytoplasmically oriented in Golgi vesicles from porcine submaxillary glands.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1985

UDPglucose-ceramide glucosyltransferase from porcine submaxillary glands is associated with the Golgi apparatus.

Subcellular distribution of pig submaxillary gland UDPglucose-ceramide glucosyltransferase (EC 2.4.1.80), the enzyme which catalyses the first step during the sequential addition of carbohydrate moieties for ganglioside biosynthesis, was studied. The results presented strongly suggest that in pig submaxillary gland, the transfer of glucose on endogenous or exogenous ceramides takes place in the Golgi apparatus: the specific activity of UDPglucose-ceramide glucosyltransferase increased in parallel with the activity of a known marker of the Golgi apparatus, UDPgalactose-ovomucoid galactosyltransferase. The specific activity of the glucosyltransferase was 18-times higher in the purified Golgi membranes than in the postnuclear supernatant and the yield was over 30%. An apparent Km of 22 microM for UDPglucose and 54 microM for ceramides was determined. Maximal glucosylation of endogenous ceramides was achieved at pH 6.5 in the presence of NADH (1 mM) as inhibitor of pyrophosphatases and with Mn2+ (5 mM). It was found that the zwitterionic detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (Chaps) is an efficient activator for the glucosylation of exogenous ceramides.

Animals↗
PubMed1984

Evidence for coupling between transport of UDP-glucose and its synthesis by membrane-bound pyrophosphorylase in Golgi apparatus of cat liver.

Incubation of sealed vesicles of cat-liver Golgi apparatus with UDP[14C]glucose showed that the vesicles accumulated radioactivity. After Triton X-100 treatment or sonication of washed vesicles, soluble radiolabeled species were released and identified by paper chromatography as UDP[14C]glucose, [14C]glucose 1-phosphate and free glucose. In the incubation medium, UDPglucose was effectively protected by addition of dimercaptopropanol and UTP. Presence of glucose 1-phosphate and glucose within the vesicles most probably arose from luminal pyrophosphatase and phosphatase. A portion of the [14C]glucose moiety became covalently linked to endogenous acceptors. Uptake of UDPglucose was saturable and dependent on time and on the concentration of sugar nucleotide. Together, these results were consistent with a transport system for UDPglucose in Golgi vesicles. Furthermore, penetration rate was considerably higher with UDPglucose synthetized in situ from glucose 1-phosphate by membrane-bound pyrophosphorylase than from added UDPglucose: Vmax values were respectively 10 and 2 pmol/15 min per mg protein. This result allows the conclusion that a coupling between translocase and synthetase is involved in UDPglucose transport through Golgi apparatus membranes. The mechanism of this 'kinetic advantage' is discussed.

Animals↗
PubMed1983

Properties of uridine diphosphate glucose pyrophosphorylase from Golgi apparatus of liver.

Golgi apparatus isolated from cat liver contained UDPglucose pyrophosphorylase (UTP:alpha-D-glucose-1-phosphate uridylyltransferase, EC 2.7.7.9) activity. The results of washing suggested that pyrophosphorylase was bound firmly to Golgi membranes. Moreover, the enzyme was activated by Triton X-100 in the same extent as galactosyltransferase, a typical Golgi apparatus enzyme. Two-substrate kinetic studies were performed with the enzymes from cytosol and Golgi fractions. The soluble enzyme showed an apparent 2.5-fold greater activity for the glucose 1-phosphate than for UTP, while pyrophosphorylase of Golgi apparatus had the same affinity for the two substrates. A random mechanism was observed with a direct dependence of apparent Michaelis constant values on the concentration of second substrate for soluble enzyme. In contrast, with Golgi enzyme one ligand had no effect on the binding of the other.

Animals↗
PubMed1979

[Comparative study of microsomal enzymic activities in adult and foetal monkey hepatocytes (author's transl)].

Differential centrifugation was applied to adult and foetal liver of monkey. Obtained fractions were: F1 (800 X g); F2 (12 500 X g); F3 (200 000 X g); and cell sap. Analysis of chemical compounds of these fractions shows that: (1) adult and foetal nucleic acids levels are similar; (2) there are more proteins in adult than in foetal hepatocytes; (3) most of the glycogen is located in F3; the foetal level is twenty times higher than the adult level. Plasma membrane enzymes (5'-nucleotidase, adenylate cyclase) show a nucleomicrosomic distribution. The distribution of alkaline phosphatase is not significant. Mitochondrial enzymes (monoamine oxydase, succinate cytochrome c reductase, cytochrome oxydase) are enriched in F2 without any sedimentation in F3. There is more malate dehydrogenase liberated in cell sap during foetal liver fractionation. This indicates the foetal mitochondria are more sensitive to the homogenisation method. Lysosomal enzymes (acid phosphatase, N-acetylglucosaminidase) are enriched in F2. The same observation for N-acetylglucosaminidase as for malate dehydrogenase leads to the same conclusion for foetal lysosomes. Endoplasmic reticulum and Golgi enzymes (glucose-6-phosphatase and related phosphotransferase activity, NADPH-cytochrome c reductase and sialytransferase) are much enriched in F3. Thus this fraction F3 is pure enough to allow the observation of the modification produced on endoplasmic reticulum and Golgi apparatus during foetal and neonatal development.

Aging↗
PubMed1979

[Monkey liver microsomal glucose-6-phosphatase].

Kinetic studies indicate that glucose-6-phosphatase is a multifunctional enzyme. a) Phosphohydrolase activities. The mannose-6-phosphatase activity is low (Km = 8 mM, VM = 90 nmoles. min-1mg-1). The enzyme shows a strong affinity for glucose-6-phosphate (Km = 2.5 mM, VM = 220 nmoles.min-1mg-1). beta-glycerophosphate (K1 = 30 mM), D-glucose (Ki = 120 mM) are mixed type inhibitors; pyrophosphate (Ki = 2 mM) is a non competitive one. b) Phosphotransferase activities. Di and triphosphate adenylic nucleosides or phosphoenol pyruvate are not substrates. Carbamylphosphate serves as a phosphoryl donor with D-glucose as acceptor. The phosphate transfer is consisstent with a random mechanism in which the binding of one substrate increases the enzymes affinity for the second substrate. Apparent Km values for carbamyl-phosphate range from 5.2 mM (D-glucose concentration leads to infinity) to 8 mM (D-glucose concentration leads to 0). The corresponding apparent Km values for D-glucose are 59 mM (carbamyl-phosphate concentration leads to infinity) to 119 mM (carbamyl-phosphate concentration leads to 0). Maximal reaction velocity with infinite levels of both substrates is 270 nmoles.min-1.mg-1. Pyrophosphate is a poor phosphoryl donnor (Km = 55 mM with D-glucose concentration 250 mM). In addition we do not find any latency; detergents, namely sodium deoxycholate, Triton X 100 do not affect or inhibit glucose-6-phosphatase activity.

Animals↗
PubMed1976

[Sialyltransferase in human malignant melanoma].

A glycosyltransferase, CMP-N-acetylneuraminic acid : glycoprotein sialyltransferase was found in human malignant melanoma. Activities were measured with desialized glycoprotein as an exogenous acceptor. The enzyme was characterized by means of its pH optimum, 5.5, temperature optimum, 30 degrees C, KM values, 10 muM for the sugar nucleotide and 0.3 mM for desialized glycoprotein. It did not require exogenously added metal ions but was slightly stimulated by Mg2+. It required detergent for optimal activity. The effect of nucleotides and sugar nucleotides on enzyme activity has been investigated.

Enzyme Activation↗
PubMed1976

[Galactose transfer in the membranes of human milk fat globules (author's transl)].

Galactosyltransferase which catalyzes the transfer from UDP-galactose to either endogeneous glycoproteins, free N-acetylglucosamine or N-acetylglucosaminyl residues in the carbohydrate portion of glycoproteins, or to glucose when alpha-lactalbumin is added, occurs in human milk fat globule membranes. Various treatments (washing of membranes, freezing and thawing) did not affect this activity. In the presence of Triton X-100, the enzyme shows appreciable latency, This detergent was then used to solubilize the enzyme and to study its main characteristics. A competition and a heat stability experiment show that only one enzyme acts on two substrates (free N-acetylglucosamine or desialyzed and degalactosylated fetuin). UDP-galactose hydrolase activities were very low compared to those of the bovine milk fat globule membranes. Other characteristic enzymes of Golgi vesicles were found in human milk fat globules membranes. It is of interest to find out whether this is the result of contamination with cytoplasmic particles or whether it reflects the participation of Golgi vesicles in human milk fat globule secretion.

Enzyme Activation↗
PubMed1976

[Amino acid incorporation by human milk fat globules membranes (author's transl)].

Human milk fat globule membranes (MFGM) can incorporate radioactive 14C amino acids in a hot trichloracetic acid-insoluble material. Aspecific adsorption and bacterial contamination are unlikely. The products of protein synthesis were analyzed by polyacrylamide gel electrophoresis in sodium dodecyl sulfate or by action of proteolytic enzymes. Various inhibitors of protein synthesis were assayed. Fragments of rough endoplasmic reticulum or mitochondria could be involved in this incorporation.

Amino Acids↗