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Biomedical subjects

G Fortier

Publications and source records attributed to G Fortier.

35 records · Page 2Linked to original sources
PubMed1990

Kinetic study of nucleophile specificity in dipeptide synthesis catalyzed by clostridiopeptidase B.

The kinetic parameters of Clostridiopeptidase B-catalyzed aminolysis of carbobenzoxyarginyl methyl ester leading to the formation of various dipeptides are investigated. The deacylation rates of the acylenzyme were evaluated by direct product analysis using high-performance liquid chromatography on a reversed-phase column. On the basis of the partitioning ratio and the first-order and second-order rate constants for the deacylation step, large differences in the nucleophile reactivities, which appear to be related to a S'1-P'1 interaction, were observed. The order of specificity was established as Leu much greater than Ser greater than Phe greater than Val greater than Ala = Gly much greater than Pro with second-order rate constants ranging from 578,614 M-1 s-1 for leucinamide to 5132 M-1 s-1 in the case of prolinamide. All of the amino acid amides had a nucleophilic strength at least 10 times higher than that of water during the deacylation step. The data reported here represent the first experimental evidence for the existence of a S'1 site engaged in the recognition of the amino acid side chain residue for this enzyme. The recognition site showed an increase in the affinity along with an increase in the hydrophobicity of the amino acid amide side chains.

Amino Acids↗
PubMed1990

Optimization of a polypyrrole glucose oxidase biosensor.

An amperometric glucose biosensor was fabricated by the electrochemical polymerization of pyrrole onto a platinum electrode in the presence of the enzyme glucose oxidase in a KCl solution at a potential of +0.65 V versus SCE. The enzyme was entrapped into the polypyrrole film during the electropolymerization process. Glucose responses were measured by potentiostating the enzyme electrode at a potential of +0.7 V versus SCE in order to oxidize the hydrogen generated by the oxidation of glucose by the enzyme in the presence of oxygen. Experiments were performed to determine the optimal conditions of the polypyrrole glucose oxidase film preparation (pyrrole and glucose oxidase concentrations in the plating solution) and the response to glucose from such electrodes was evaluated as a function of film thickness, pH and temperature. It was found that a concentration of 0.3 M pyrrole in the presence of 65 U/ml of glucose oxidase in 0.01 M KCl were the optimal parameters for the fabrication of the biosensor. The optimal response was obtained for a film thickness of 0.17 microns (75 mC/cm2) at pH 6 and at a temperature of 313 K. The temperature dependence of the amperometric response indicated an activation energy of 41 kJ/mole. The linearity of the enzyme electrode response ranged from 1.0 mM to 7.5 mM glucose and kinetic parameters determined for the optimized biosensors were 33.4 mM for the Km and 7.2 microA for the Imax. It was demonstrated that the internal diffusion of hydrogen peroxide through the polypyrrole layer to the platinum surface was the main limiting factor controlling the magnitude of the response of the biosensor to glucose. The response was directly related to the enzyme loading in the polypyrrole film. The shelf life and the operational stability of the optimized biosensor exceed 500 days and 175 assays, respectively. The substrate specificity of the entrapped glucose oxidase was not altered by the immobilization procedure.

Biosensing Techniques↗
PubMed1988

Effect of magnesium on ATP labelling by kidney brush border membrane.

1. Brush border membranes purified from rat kidney cortex were incubated in the presence of ATP and analysed by SDS polyacrylamide gel electrophoresis. 2. Quantitative analysis of phosphorylation was performed with a calibration curve obtained by autoradiography. 3. The presence of magnesium was required for the phosphorylation of membrane proteins. 4. EDTA completely inhibited the labelling of all bands, except for the alkaline phosphatase band. 5. In contrast, alkaline phosphatase was inhibited by 52, 65 and 85% in the presence of 1 mM bromotetramisole, 10 mM NaF and 10 mM Na arsenate respectively. 6. However these inhibitors had only minor effects on the labelling of other proteins. 7. High concentrations of magnesium caused a pronounced inhibition on the labelling of the alkaline phosphatase band but had no effect on the phosphorylation of other proteins.

Adenosine Triphosphate↗
PubMed1988

[Intestinal angiostrongyliasis caused by Angiostrongylus costaricencis. Apropos of a case in Martinique].

Intestinal angiostrongyliasis caused by Angiostrongylus costaricensis is a rare nematodiasis which is present mainly in Costa-Rica, and in some other countries in the northern part of South America, Central America, and in the southern part of Mexico. This is a report of the first case from Martinique involving a sixteen month old child, and proved by an intestinal pathologic study. The epidemiology of the disease, its clinical, parasitological, histopathologic and therapeutic aspects are emphasized.

Angiostrongylus↗
PubMed1987

Analysis of amino acids by gas-liquid chromatography as tert.-butyldimethylsilyl derivatives. Preparation of derivatives in a single reaction.

The effect of temperature, solvent and reagents on the formation of the N(O)-dimethyl-tert.-butylsilyl derivatives of proteic amino acids has been studied. Quantitative silylation is achieved using dimethyl-tert.-butylsilyltrifluoroacetamide with 1% tert.-butyldimethylchlorosilane in dimethylformamide by heating at 75 degrees C for 30 min. Two peaks were obtained for arginine under these conditions. However, most of the standard proteic amino acids can be assayed. The N(O)-dimethyl-tert.-butylsilyl derivatives of the proteic amino acids have been analysed by gas chromatography-mass spectrometry using the methane chemical ionization mode. The spectral data are presented and have been used to confirm the structures of the amino acid derivatives.

Amino Acids↗
PubMed1986

Identification of a new, naturally occurring, non proteic amino acid in xylem sap of Pisum sativum.

The xylem sap of nitrogen-fixing Pisum Sativum cv Homesteader has been examined by capillary gas chromatography and by gas chromatography mass spectrometry in both electron-impact and chemical ionization modes following the formation of N-heptafluorobutyryl isobutyl ester derivatives. One of the compounds thus detected had a mass of 389 and contained chlorine, one carboxylic acid group and a nitrogen atom. High-resolution mass spectrometry indicated that there were no other hetero atoms present in the molecule. The composition was determined to be C4H8NO2Cl. This composition can be explained only in terms of a chloroamino butyric acid.

Amino Acids↗
PubMed1985

[Malnutrition and anemia in children hospitalized in Martinique].

In order to assess prevalences, characteristics and risk factors of malnutrition and anemia, a clinical and biological study was undertaken at Lamentin hospital in 100 hospitalized children aged 6 months to 6 years. Forty seven p. cent of children were underweight and 38 p. cent were anemic. Anemia and iron deficiency predominated in the under-24-month age group, whereas wasting was the dominate finding in older children. Under 2 years of age, risk factors for wasting and anemia were associated with method of breastfeeding. Over 2 years of age, low birthweight was the only risk factor of wasting identified. In Martinique, nutritional deficiency is common in children admitted to hospital and a high index of suspicion is indicated in the hospitalized population. Following the resolution of infections, supplemental iron therapy must be considered for a great number of children under 2 years of age.

Anemia↗
PubMed1978

[Laron type familial dwarfism; genetic primary somatomedin deficiency].

Five children from 3 different families presented with severe dwarfism and the morphological and biological features described by Laron: familial occurrence, small stature, peculiar facies, high levels of plasma HGH and resistance to treatment by GH. This therapeutic inefficiency is expressed by an absence of physical growth and unchanged nitrogen balance, during a prolonged treatment. The plasma levels of somatomedine were very low (K. Hall's biological method) and not influenced by administration of exogenous HGH. These findings suggest that the fundamental disorder is not an abnormal structure of the molecules of GH. This hypothesis seems further confirmed by the structural analysis of plasma HGH, which gave the same results as those of the reference GH.

Child↗
PubMed1976

[A rare tumour of the right hypochondrium in the child (author's transl)].

Pancreatic pathology in the child is rare and usually limited to necrotic or traumatic pseudo-cysts. The authors report a case of multicystic dysplasis localised in the pancreas in a one-year old infant. The preoperative diagnosis of a traumatic cyst was made in error as the result of the discovery of a fracture of the skull. At operation, the "tumour" was seen to be a multicystic mass within the duodenal loop but pediculated under the inferior surface of the pancreas. Histological examination confirmed its dysplasic nature. The presence, as a result of vascular compression, together with the post-operative resolution of hypertension lend further originality to this case.

Diagnosis, Differential↗
PubMed1975

[Current status of teaching pediatrics in France in the medical curriculum].

On the basis of a surgery performed by a questionnaire sent to all French medical schools (44, out of them 30 replied), the authors describe the current status of the teaching of pediatrics at undergraduate level. The 1970 reform, introducing a block teaching system, made easier to teach pediatrics made easier to teach pediatrics as an autonomous entity. But it leaves a lot to do with a view to improving the situation - in spite of the excessive number of students - by a better definition of the pedogogical objectives, a better integration of basic sciences, a broader place for small group and bedside teaching, a greater emphasis on the social aspects of pediatrics, and by the organisation, for the more motivated students, of optional courses.

Curriculum↗