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Biomedical subjects

B Michel

Publications and source records attributed to B Michel.

At least 109 records · Page 6Linked to original sources
PubMed1990

[Encephalopathy caused by prions].

The concept of prion encephalopathy has emerged from such previous notions as slow virus infections, spongiform encephalopathies or transmissible dementias. The term prion (Prusiner, 1982) is now used in preference to unconventional agents. Proteins and genes of prions have recently been identified by molecular biology. Exactly how prion proteins are amplified in cells is still unknown. It has been demonstrated that amyloid deposits in scrapie-infected brain, Creutzfeldt-Jakob, Gerstmann-Straüssler and Kuru diseases are composed of prion proteins. Prion encephalopathies are good models to study some immunopathological mechanisms observed in the central nervous system in degenerative diseases or ageing.

Amyloidosis↗
PubMed1989

In vitro binding of the bacteriophage f1 gene V protein to the gene II RNA-operator and its DNA analog.

We have investigated the binding of the f1 single-stranded DNA-binding protein (gene V protein) to DNA oligonucleotides and RNA synthesized in vitro. The first 16 nucleotides of the f1 gene II mRNA leader sequence were previously identified as the gene II RNA-operator; the target to which the gene V protein binds to repress gene II translation. Using a gel retardation assay, we find that the preferential binding of gene V protein to an RNA carrying the gene II RNA-operator sequence is affected by mutations which abolish gene II translational repression in vivo. In vitro, gene V protein also binds preferentially to a DNA oligonucleotide whose sequence is the DNA analog of the wild-type gene II RNA-operator. Therefore, the gene V protein recognizes the gene II mRNA operator sequence when present in either an RNA or DNA context.

Coliphages↗
PubMed1989

Preliminary report of familial thymic lymphosarcoma in Holstein calves.

Seventy-three cases of the thymic form of leukosis were found in Holstein calves in five departments of France over a period of five months. Most of the calves had been sired by the same bull. The calves were negative for specific antibodies to bovine leukaemia virus. Morphological studies including light and electron-microscopic cytology, and serological and virological studies of 14 of the cases suggest that the disease was transmitted genetically.

Animals↗
PubMed1989

[Wolff-Parkinson-White syndrome and verapamil: apropos of a case of ventricular fibrillation].

Numerous highly effective antiarrhythmic agents are now available which have a powerful anti-arrhythmia action but may cause severe side effects in the case of inappropriate use. We report the case of a patient with WPW syndrome in whom inappropriate administration of verapamil during an episode of atrial fibrillation and rapid ventricular response caused ventricular fibrillation.

Adult↗
PubMed1989

[Retrospective study of permanent cardiac stimulation in patients over 80 years of age].

Out of 833 pacemakers implanted between 1979 and 1983, 228 were in patients aged over 80 years (137 aged 80-84, 79 85-89, and 12 90-93). Indication for cardiac stimulation was high-grade atrioventricular (av) block in 47%, sick sinus syndrome in 38%, low ventricular response in atrial fibrillation in 13% and hypersensitivity of the carotid sinus in 1%. An average follow-up period of 29.5 months (18-78 months), focusing special interest on quality of life, revealed that of the 199 patients (87%) who were independent at the time of implantation, 29 (15%) became dependent on social services during the follow-up and during the same period 49 (21%) were rehospitalized (88 hospitalizations) for reasons other than pacemaker problems. During the first year after implantation the mortality in the "paced" population was higher than in the general population of the same age groups; thereafter the survival curves run almost parallel. Mortality does not differ between persons paced for av block of for sinus node disease. We conclude that cardiac stimulation in patients aged over 80 years allows them to preserve their lifestyle and independence when compared to the general population, with the same rate of survival.

Aged↗
PubMed1989

Binding and oxidation of mutant cytochromes c by cytochrome-c oxidase.

Mutation of conserved Phe-82 of yeast iso-1 cytochrome c to Tyr, Gly, Ser, Leu, or Ile affects binding to and reaction with cytochrome-c oxidase from beef heart. The observed changes of binding and kinetic constants reflect mutation-induced rearrangements in the heme vicinity brought about by the replacement of Phe-82. Such conformational rearrangements are also revealed by altered circular dichroism spectra of the oxidase-bound mutant cytochromes c. Variations in Km for cytochrome c oxidation do not parallel variations in Kd, the dissociation constant for binding of cytochrome c to the oxidase. This observation does not support an enzymatic mechanism in which the rate of cytochrome c oxidation is governed by product dissociation.

Animals↗
PubMed1989

The cytochrome c oxidase-cytochrome c complex: spectroscopic analysis of conformational changes in the protein-protein interaction domain.

Binding to cytochrome c oxidase induces a conformational change in the cytochrome c molecule. This conformational change has been characterized by comparing the binding of native cytochrome c and chemically modified cytochrome c derivatives to bovine cytochrome c oxidase by using absorption, circular dichroism (CD), and magnetic circular dichroism (MCD) spectroscopy. The following derivatives were analyzed: (i) cytochrome c modified at all 19 lysine residues to yield the (N epsilon-acetimidyl)19 cytochrome c, (N epsilon-isopropyl)19 cytochrome c, and (N epsilon,N epsilon-dimethyl)19 cytochrome c; (ii) cytochrome c in which Met65 and Met80 are converted to the methionine sulfoxide; (iii) cytochrome c with a single break in the polypeptide chain at Arg38 or Gly37. The derivatives bind to cytochrome c oxidase at a ratio of one heme c per heme aa3. The association constants are similar to that of native cytochrome c except for (N epsilon-isopropyl)19 and (N epsilon,N epsilon-dimethyl)19 cytochromes c, which bind respectively four times and six times less strongly. The derivatives are good substrates for the cytochrome c oxidase reaction. The spectral changes accompanying the binding of the modified cytochromes c to cytochrome c oxidase are quite different from the spectral changes observed with native cytochrome c. The different optical absorption and MCD changes are explained by a polarity change around the exposed heme edge in the cytochrome c-cytochrome c oxidase complex. The CD changes indicate a conformational rearrangement restricted to the surface area surrounding the exposed heme edge. The rearrangement may involve a movement of the evolutionarily conserved Phe82 out of the vicinity of the heme.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Oxidation of cytochrome c by cytochrome c oxidase: spectroscopic binding studies and steady-state kinetics support a conformational transition mechanism.

The long-known biphasic response of cytochrome c oxidase to the concentration of cytochrome c has been explained, alternatively, by the presence of a catalytic and a regulatory site on the oxidase, by negative cooperativity between adjacent active sites in dimeric oxidase, or by a transition of the enzyme molecule between different conformational states. The three mechanistic hypotheses allow testable predictions about the relationship between substrate binding and steady-state kinetics catalyzed by the monomeric and dimeric (or oligomeric) enzyme. We have tested these predictions on monomeric, dimeric, and oligomeric beef heart oxidase and on monomeric oxidase from Paracoccus denitrificans. The aggregation state of the oxidase was evaluated from the sedimentation equilibrium in the ultracentrifuge and by gel chromatography. The binding of cytochrome c to cytochrome c oxidase was measured by spectrophotometric titration of cytochrome c oxidase with cytochrome c. The procedure makes use of a small perturbation in the Soret band of the absorption spectrum of the cytochrome c-cytochrome c oxidase complex. The steady-state oxidation of cytochrome c was followed spectroscopically by an automated assay procedure, and the kinetic parameters were deduced by numerical analysis of several hundred initial rate assays in the substrate concentration range 0.15-30 microM. The following results were obtained: (1) The kinetics of cytochrome c oxidation are always biphasic at low ionic strength, independent of the aggregation state of the enzyme. (2) The kinetics become apparently monophasic at ionic strengths above 100 mM or at slightly acidic pH values.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Binding modes of IgG from pemphigus autoimmune sera onto guinea pig keratinocytes and the fate of bound IgGs.

Pemphigus is an intraepidermal autoimmune blistering disease of humans caused by circulating IgGs. We have investigated the binding mode and the fate of bound antibodies from Pemphigus sera (P-IgG) on guinea pig keratinocytes in suspension in order to find clues to the loss of cell adhesion in vivo (acantholysis). Flow cytometry, following indirect immunofluorescent labeling of the keratinocytes, and dead cells' staining with ethidium bromide, demonstrated the specific surface binding of P-IgG onto living keratinocytes only. This was shown with several Pemphigus sera or purified P-IgG. This technique, used with various Pemphigus sera, showed that the specific binding is increased when the serum titer is higher, and "Km" values for P-IgG were roughly and inversely correlated to the titers. Upon saturation the same average number of Pemphigus IgG sites per cell were found for the sera of different patients. Analysis of the specific binding of [125I]-P-IgG onto Percoll-separated (living) keratinocytes showed the existence of two classes of sites: 2 x 10(6) sites/cell high-affinity sites (Kd = 1.5 x 10(-6) M total IgG) and 25 x 10(6) sites/cell low-affinity sites (Kd = 6 x 10(-5) M total IgG). Cell sorting and flow cytometry of individual cells allowed us to correlate the light-scattering signal, the RNA content, the size and morphology, and the P-IgG binding to the cells. The results indicated that P-IgG binding is homogeneous within the living keratinocytes and increases with cell size (cell maturity). Cell-sorter analysis of cells with membrane-bound P-IgG, coupled to direct determination of P-IgG released in the medium, revealed the fate of bound P-IgG: 40-60% of the P-IgGs were released in the medium within 30 minutes at 37 degrees C. This was accompanied and followed by a much slower, metabolic energy-dependent, internalization process of the membrane-bound P-IgG. The internalization has been confirmed by electron microscopy of bound P-IgG labeled with protein A-gold. Internalized IgGs were seen in the cells in coated membranous vesicles and other endocytic compartments. Similar behavior was also observed with two other membrane ligands: i.e., concanavalin A and multispecific rabbit "antisurface" antibodies.

Animals↗
PubMed1989

IgA pemphigus foliaceus. Report of two cases and a review of the literature.

The cases of two patients with vesiculobullous lesions were diagnosed clinically and histopathologically as pemphigus foliaceus; unexpectedly, both revealed intercellular IgA, but not IgG, in the upper epidermis by direct immunofluorescence. Such histologic and immunofluorescence findings have been reported in eight other cases. In our cases no circulating IgA or IgG intercellular antibodies could be detected; in four of eight other reported cases IgA antibodies showed intercellular staining like that of pemphigus antibodies. Subcorneal acantholytic lesions occurred in both our cases; of the other cases reported, five had essentially identical histopathologic findings. The clinical and histopathologic features of pemphigus, as well as the recent findings of circulating IgA intercellular antibodies alone or with IgG antibodies, appear to place this disease into the spectrum of pemphigus. The 10 IgA pemphigus cases reported to date fall into one of two groups, the IgA pemphigus foliaceus (including our two cases) and IgA pemphigus of the intraepidermal neutrophilic type, which seems to be less common.

Adult↗
PubMed1989

Translational repression in bacteriophage f1: characterization of the gene V protein target on the gene II mRNA.

Previous studies have shown that the single-stranded DNA binding protein of bacteriophage f1 (gene V protein) represses the translation of the mRNA of the phage-encoded replication protein (gene II protein). We have characterized phage mutations in the repressor and in its target. Using a gene II-lacZ translational fusion, we have defined a 16-nucleotide-long region in the gene II mRNA sequence that is required in vivo for repression by the gene V protein. We have shown that in vitro the binding affinity of the gene V protein is at least 10-fold higher to an RNA carrying this sequence than to an RNA lacking it. We propose that this sequence constitutes the gene II mRNA operator.

Base Sequence↗
PubMed1989

Deletion hot spots in chimeric Escherichia coli plasmids.

Deletions form frequently in chimeric plasmids composed of M13mp2, pBR322, and pC194 (B. Michel and S. D. Ehrlich, Proc. Natl. Acad. Sci. USA 83:3386-3390, 1986). They are generated by joining of the nucleotide neighboring the nick site in the M13 replication origin to a nonadjacent nucleotide. This nucleotide is most often located within particular short plasmid regions, named deletion hot spots. Three natural hot spots were present in the chimeric plasmids. Two were active only when the DNA replication initiated at the M13 origin was allowed to progress; the third was active only in the presence of wild-type amounts of DNA ligase. Three artificial hot spots were generated by creating palindromic sequences in the plasmids.

Base Sequence↗
PubMed1989

[Abnormal postural movements: transient ischemic episodes of the carotid?].

Following post-operative occlusion of the right internal carotid artery, a 65-year old man developed abnormal left involuntary movements which appeared in upright position or at exercise and disappeared in sitting or supine positions. The clinical and electroencephalographic features of these movements could have been epileptic. However, this case together with data from the literature suggest that transient ischemic episodes in the carotid territory may be expressed as involuntary movements occurring in certain positions, betraying a severe and abrupt fall in cerebral blood flow.

Aged↗
PubMed1988

Copy choice illegitimate DNA recombination.

Precise excision of Tn10 and related transposons occurs by recombination between directly repeated 9 bp sequences that flank the transposon. The excision, which is a model for a class of illegitimate DNA recombination events, was stimulated 10(6) times by induction of single-stranded DNA synthesis, occurred during conversion of single-stranded DNA to double-stranded form, and entailed no transfer of physical material from parental to progeny molecules. We conclude that it occurred by copy choice DNA recombination and suggest that other illegitimate recombination events may occur by a similar mechanism.

Coliphages↗