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Biomedical subjects

M Laurent

Publications and source records attributed to M Laurent.

At least 199 records · Page 11Linked to original sources
PubMed1985

Analysis of progress curves for a highly concentrated Michaelian enzyme in the presence or absence of product inhibition.

Methods are given for analysing the time course of an enzyme-catalysed reaction when the concentration of the enzyme itself is high, a situation which is often found in vivo. (1) The integrated form of the kinetic equation for a concentrated Michaelian enzyme in absence of product inhibition is given. Parameters are shown to be calculated easily using non-linear fitting procedures. (2) A general algorithm to analyse progress-curve data in more complex cases (i.e. when the analytical form of the integrated rate equation is not known or is exceedingly complex) is proposed. This algorithm may be used for any enzyme mechanism for which the differential form of the kinetic equation may be written analytically. We show that the method allows differentiation between the main types of product inhibition which may occur in the case of a highly concentrated Michaelian enzyme.

Enzyme Inhibitors↗
PubMed1985

Amino acid sequence of the non-collagenous globular domain (NC1) of the alpha 1(IV) chain of basement membrane collagen as derived from complementary DNA.

NC1, the C-terminal non-collagenous globular domain of collagen IV, represents one of the two end regions responsible for the assembly and cross-linking of the extracellular network of basement membrane collagen. Several cDNA clones for the NC1 domain of the alpha 1(IV) collagen chain of mouse have been isolated by using synthetic oligonucleotides as screening probes for mouse libraries. The oligonucleotides were synthesized according to known stretches of the corresponding protein sequence. Sequencing of the overlapping cDNA clones allowed the complete amino acid sequence of the NC1 domain to be deduced as well as the C-terminal 165 amino acid residues of the triple helix. It consists of 229 amino acid residues which comprise two homologous regions with a high content of cysteine. These DNA and protein sequences are compared to the corresponding sequences of other collagens and discussed with respect to their structural and biological significance.

Amino Acid Sequence↗
PubMed1985

Recombinant DNA techniques: storage and screening of cDNA libraries with large numbers of individual colonies from initial transformations.

A typical cDNA library with a large number of initial transformants, plated in soft agarose, can be stored and shipped in 12% glycerol at -70 degrees C. To prepare the library for storage, the soft agarose layer is made into a paste and the agarose is removed by Sephadex G-25 filtration. This method of cDNA library storage does not alter the relative representation of the plasmids carried in the library. To achieve a very uniform distribution of colonies at high colony density, an aliquot of the cDNA library is diluted to 3000 to 10,000 colonies/ml. One milliliter of this suspension is evenly distributed on a nitrocellulose filter on an agar plate and air-dried. Filter copies are made and screened by published methods.

Cloning, Molecular↗
PubMed1985

[Idiopathic ventricular arrhythmia in children. Apropos of 24 cases].

The severity and prognosis of idiopathic ventricular arrhythmias in childhood were studied in 24 patients (12 boys, 12 girls) with an average age of 8 years at the time of diagnosis of the arrhythmia. Investigations included clinical assessment and analysis of basal ECG (morphology of the arrhythmias) and dynamic recordings (Holter and exercise stress testing). The clinical course was followed for an average of 3.8 years. The patients were classified in two groups: monomorphic arrhythmias (Group I) and polymorphic arrhythmias (Group II). Group I was divided into 4 subgroups: isolated ventricular extrasystoles (IA), 11 patients; ventricular extrasystoles with bursts of ventricular tachycardia (IB), 6 patients; sustained ventricular tachycardia without intercritical extrasystoles (IC), 1 patient; accelerated idioventricular rhythm (ID), 2 patients. Subgroups IA, IB and ID were characterised by the absence of symptoms, the disappearance of the arrhythmia on exercise, the decreased efficacy of antiarrhythmic drugs and an excellent prognosis. Therapeutic abstention was the rule in these patients. Patients in Group IC were characterised by the variability of their symptoms, the absence of exercise induced arrhythmias, the need for treatment in most cases and a good long-term prognosis. Group II was divided into 2 subgroups: adrenergic polymorphic ventricular tachycardia (IIA), 2 patients, and non-adrenergic polymorphic ventricular tachycardia (IIB), 2 patients. Patients in Subgroup IIA were characterised by syncope on exercise or emotion, the need for betablocker therapy which considerably improved the patients symptoms but which did not usually prevent sudden death.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1985

[Accelerated idioventricular rhythm. 2 new cases in children].

Two new cases of idiopathic accelerated idioventricular rhythm are reported in children aged 12 and 16. This is a very rare arrhythmia in childhood with only 12 previously published cases in the medical literature. The prognosis seems to be excellent in all cases which underlines the importance of distinguishing this rhythm from other ventricular arrhythmias observed in childhood.

Adolescent↗
PubMed1985

[Light chain disease with terminal myocardiopathy].

The authors report a case of a 35 year old man with of congestive cardiac failure. Echocardiography showed diffuse hypokinetic wall motion with moderate parietal hypertrophy without dilatation. Post-mortem examination showed intramyocardial deposits of light chains identical to those observed in "in vivo" renal and liver biopsies. This rarely described disease has a poor prognosis. It is characterised by polyvisceral infiltrations of light chain monoclonal immunoglobulins. Renal disease is usually the main problem progressing rapidly to renal failure. Of the extra renal localisations, cardiac involvement would appear to be common and preoccupying in itself. Monoclonal plasmocytic proliferation is observed in all cases, the majority but not all being malignant (myeloma). The incidence of this condition is probably underestimated and may pass undetected if immunofluorescent techniques are not used. Myelomatous light chain cardiac disease could therefore be more common than amyloidosis with which it presents a number of common features.

Adult↗
PubMed1984

Translocation alters the activation rate of a trypanosome surface antigen gene.

We report here the characterization of the gene coding for AnTat 1.13, a very late variable antigen type (VAT) from Trypanosoma b. brucei. This gene is chromosome-internal and it is activated by the duplicative mechanism. Like in another case of late VAT expression (1), its expression-linked copy (ELC) is flanked by "companion" sequences. It was possible to convert the late expression of this VAT into an early one, by changing the location of the gene in the genome. This has been achieved by selecting an AnTat 1.6 clone among heterotypes arising in the AnTat 1.13 cloned population. Indeed, this particular derivation leads to the conservation of the AnTat 1.13 ELC as a new telomeric member of the gene family, and this conserved ELC (or ex-ELC) appears to be preferentially activable. The telomeric position and other factors possibly involved in early or late antigen gene expression are discussed; in this respect, we propose that some antigen genes are rarely activated because their duplicative transposition requires the presence, in the expression site, of "companion" sequences only shared by a limited number of other genes.

Animals↗
PubMed1984

Possible DNA modification in GC dinucleotides of Trypanosoma brucei telomeric sequences; relationship with antigen gene transcription.

Polymorphism in restriction site cleavage (PstI, SphI, PvuII, HindIII) has been noticed in several occasions in the telomeric sequences harbouring trypanosome variant-specific antigen genes (1, 2, 3). This polymorphism has been further investigated and seems best interpreted as due to partial DNA modification in GC dinucleotides. The actively transcribed telomeric genes do not exhibit such a polymorphism; furthermore, in at least three independent cases, gene inactivation is linked to the appearance of polymorphism. It could thus be hypothesized that DNA modification prevents antigen gene transcription, or vice-versa. We report however that at least some telomeric antigen-specific sequences of the procyclic trypanosomes (in vitro culture form) are not polymorphic, although they do not synthesize any variant-specific antigen mRNA. There is thus no absolute relationship between the absence of polymorphism and antigen gene transcription.

Animals↗
PubMed1984

Apparent co-operativity for highly concentrated Michaelian and allosteric enzymes.

The effect of high enzyme concentration on velocity curves is analysed quantitatively for both Michaelian and simple allosteric enzymes. The general principles and practical approaches developed here are applicable to other models and may provide information on enzyme function in vivo. At physiological enzyme concentrations. Michaelian enzymes display amplification properties of the same magnitude as those observed for allosteric enzymes. In terms of apparent co-operativity, this corresponds to Hill coefficients that are locally much larger than the number of interacting or non-interacting binding sites. However, compared to the Michaelian case, allosteric interactions are needed to provide a combination of both positive and negative apparent co- operativities . These effects are important for understanding the biological significance of intersubunit cooperation in oligomeric enzymes.

Allosteric Regulation↗
PubMed1984

Solution X-ray scattering studies of the yeast phosphofructokinase allosteric transition. Characterization of an ATP-induced conformation distinct in quaternary structure from the R and T states of the enzyme.

The allosteric transition of yeast phosphofructokinase has been studied by solution x-ray scattering. The scattering curves corresponding to the native enzyme (T conformation) were found to be similar to the curves recorded in the presence of saturating concentrations of fructose 6-phosphate (R conformation) or AMP (R or R' conformation). However, the curves obtained in the presence of ATP are clearly different: the radius of gyration increases and the secondary minima and maxima are systematically shifted to lower angles, suggesting a swelling of the enzyme in the presence of ATP. These results give the first direct evidence for the existence of an ATP-induced T' conformation, distinct in quaternary structure from the R and T states of the enzyme oligomer, in agreement with our previous modeling of yeast phosphofructokinase regulation. X-ray scattering data are discussed in relation to the distinct molecular mechanisms of the ATP and fructose 6-phosphate allosteric effects involving, respectively, sequential and concerted conformational changes of the enzyme oligomer.

Allosteric Regulation↗
PubMed1984

Studies on the structure of yeast phosphofructokinase.

In this paper, we describe an efficient procedure for the purification of yeast phosphofructokinase. This procedure eliminates any time delay and enables to obtain an enzyme with minimum proteolytic alterations. The molecular weights of the oligomeric enzyme and of its constitutive subunits were both evaluated by means of several independent methods. However, the accuracy of each measurement was not sufficient to discriminate between an hexameric and an octameric structure of the enzyme oligomer. On the other hand, crosslinking experiments demonstrated the octameric structure of yeast phosphofructokinase. Obviously, some methods of molecular weight determination have led to erroneous results. In particular, our experiments show that the reliability of molecular weight determinations performed by gel filtration of native proteins must be considered with caution.

Cross-Linking Reagents↗
PubMed1984

Effect of taurocholic acid feeding on methyl-nitro-N-nitroso-guanidine induced gastric tumors.

Bile reflux is generally accepted as a causative factor of gastric cancer after partial gastrectomy. The present study was designed to evaluate the promotion, by the per oral administration of taurocholic acid, of methyl-N-nitro-N'-nitrosoguanidine (MNNG)-induced gastric carcinogenesis. MNNG (83 mg/l) was given in the drinking water to half the male Wistar rats during 12 weeks while the other half served as controls. After this treatment half of the MNNG-treated animals and half of the controls were placed under a diet containing 0.2% of taurocholic acid while the other animals received the standard diet. At the 40th week after initiation of MNNG, surviving animals were killed. Their stomachs and their duodenums were observed for macro and microscopic examination. Macroscopically there were 7 animals bearing gastric tumors in the MNNG group and 15 in the MNNG + bile group (P less than 0.05). Microscopically there were 7 animals with severe antral dysplasia in the MNNG group, 7 rats with fundic dysplasia and 18 with severe antral dysplasia in the MNNG + bile group. Both groups developed an identical number of duodenal tumors which were invasive adenocarcinomas or angiosarcomas. In this experiment taurocholic acid significantly promoted gastric carcinogenesis. It is postulated that surgical techniques inducing duodenal reflux in the stomach may produced a 'high risk' group of patients in which a long and careful follow-up is required.

Adenocarcinoma↗
PubMed1983

Differential size variations between transcriptionally active and inactive telomeres of Trypanosoma brucei.

We have studied the genes coding for the variant-specific surface antigen (VSA) in a series of seven trypanosome clones derived from AnTat 1.1: 1.1 leads to 1.3 leads to 1.6 leads to 1.16 leads to 1.1C leads to 1.3B leads to 1.18 These genes are all telomeric (1-5), and their surrounding, although sometimes similar, differs in each case. The length between these antigen genes and the corresponding DNA end appears to increase at each antigenic switch, with however occasional sharp size reductions, often linked to the involvement of the telomere in gene expression. This increase is due to a constant "growth" of the telomeres, at a rate of about 28 bp per day in at least four cases and probably linked to chromosome duplication. The telomere harbouring the transcribed VSA gene is growing slightly faster (about 36 bp per day), and it is the only one whose size reduction is progressive, leading to a terminal length heterogeneity within a clone. As a result, the active VSA gene is found in a population of telomeres which, as the trypanosomes divide, becomes increasingly heterogeneous, with however a preferred discrete size class about 1.4 kb smaller. The fact that the "active" telomere is the only one in a chromatin conformation highly sensitive to DNAaseI (1-4, 6), suggests that chromatin structure influences the rate and extent of both size increase and shortening of telomeres.

Animals↗
PubMed1983

Interaction of bovine epithelial lens (BEL) cells with extracellular matrix (ECM) and eye-derived growth factor (EDGF). II. Partial re-expression of the differentiated collagen distribution and phenotype.

The differentiated phenotype of bovine epithelial lens (BEL) cells consists primarily of type IV collagen production with homogeneous cellular form and monolayer organization. We have previously described how, after several subcultures, BEL cells lost this phenotype, which was replaced by a complex collagen mixture consisting predominantly of type I and type III collagens and a minor proportion of type IV collagen. The cells became irregular and formed multilayers. These dedifferentiated cells can re-express their initial morphological properties when subcultured on an extracellular matrix (ECM) in presence of an eye-derived growth factor (EDGF), as described in the first paper of this series [30]. Furthermore, those cells passaged only one time on ECM + EDGF partially re-express the native differentiated collagen phenotype. The cells synthesize a majority of type IV collagen (up to 65%) with minor amounts of interstitial collagens. As in early subcultured cells, the major proportion of total collagen accumulated in the cell layer. Taken together, the morphological and biochemical data emphasize the relationship between cell shape and collagen phenotype expression. They also provide a reversible system for the study of normal gene expression and pathological alterations.

Animals↗
PubMed1983

Modifications of a Trypanosoma b. brucei antigen gene repertoire by different DNA recombinational mechanisms.

In the Trypanosoma b. brucei AnTat 1.1C clone, the gene coding for the variant-specific surface antigen is telomeric and appears as a hybrid sequence, partially modified by gene conversion. This conversion is very similar to that observed in another AnTat 1.1-expressor clone (AnTat 1.1B). This sequence is not activated by duplicative transposition, although it could be activated by duplication in another clone (AnTat 1.10). Instead activation of the AnTat 1.1C gene seems operated by reciprocal recombination between its own telomere and the telomere carrying the previous (AnTat 1.16) ELC. Indeed, from the switch to AnTat 1.1C onward, the AnTat 1.16 ELC becomes a new silent member of its gene family, whereas in the variant directly derived from AnTat 1.1C (AnTat 1.3B), the AnTat 1.1C-containing telomere is lost, probably replaced by a large duplicate, at least 40 kb long, of the AnTat 1.3 gene-containing telomere. Different DNA rearrangement mechanisms used by the trypanosome to change its antigenic type thus contribute, by gain and loss of genes, to the evolution of the repertoire for surface antigens.

Animals↗