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Biomedical subjects

M Denis

Publications and source records attributed to M Denis.

At least 235 records · Page 13Linked to original sources
PubMed1985

Cytochrome c oxidase in plant mitochondria. Electron transfer after flash photolysis at low temperature of the CO-bound half-reduced complex.

Rebinding of CO after flash photolysis of the carboxy mixed-valence cytochrome c oxidase in plant mitochondria has been monitored in the visible range at low temperature (160-210K). At 586/630 nm, the photodissociation of the CO-saturated suspension was followed by a largely incomplete rebinding of CO to Fea3. After a series of three to four flashes, the unbound species accumulated up to 85% of the total enzyme, the remaining 15% CO-bound form undergoing recombination repetitively. In the Soret region, the absorbance level after the first flash came back to the initial one, as if all the CO-bound form were restored. However, the amount of complex which could be photodissociated by a second flash was only part of the starting material, in agreement with observations in the alpha range. The unbound species exhibited optical features very similar to the ones of compound C. The lack of CO rebinding is interpreted as due to an electron redistribution induced by the flash photolysis. This electron transfer has been tentatively assigned to a concomitant CuB oxidation and CuA reduction on the basis of the 655 nm band as a probe for a3+3 [Beinert et al. (1976) Biochim. Biophys. Acta 423, 339-355] and of the optical features in the visible range. Results are discussed with respect to analogous investigations with beef heart mitochondria and the studies by Boelens and Wever (1979-1982) of electron transfer after photolysis of the carboxy mixed-valence state when using the isolated mammalian enzyme at room temperature.

Animals↗
PubMed1985

Nontransformed rabbit liver glucocorticoid receptor: purification, characterization and transformation.

The molybdate-stabilized nontransformed form of the glucocorticoid receptor from rabbit liver has been purified approximately 8,000-fold by a three-step procedure. The first step involved protamine sulfate precipitation which allowed a 5-6-fold purification with 85% yield. The second step, affinity chromatography using a N-(12-dodecyl-amino) 9 alpha-fluoro-16 alpha-methyl-11 beta, 17 alpha-dihydroxy-3-oxo-1,4-androstadiene-17 beta-carboxamide substituted Sepharose gel, purified the receptor 1,500-2,000-fold as calculated by specific radioactivity. The third step involved high performance liquid chromatography resulting in overall purification near 8,000-fold. The final glucocorticoid receptor appeared about 60% pure. The purified nontransformed glucocorticoid receptor had a sedimentation coefficient of 9 S in 0.16 M phosphate containing 5-20% sucrose gradients and the Stokes radius was 6.1-6.3 nm as determined by low pressure gel filtration and HPLC. Binding specificity of the purified receptor was identical to that previously reported in crude rabbit liver cytosol. Isoelectricfocusing and ion-exchange chromatography showed that the purification procedure affected the net charge of the receptor protein. This phenomenon could be related to interactions between the glucocorticoid receptor and cytosolic factors. SDS polyacrylamide gel electrophoresis showed a major Mr = 94,000 protein band which is in good agreement with previously reported values for glucocorticoid receptors. Transformation of the purified receptor was achieved after removal of molybdate by exposure at 25 degrees C to 0.4 M KCl. Characterization of the molecular forms was performed by means of incorporation into isolated nuclei, affinity towards polyanionic exchangers and high pressure size exclusion chromatography. Results show that about 40% of the receptor is in the transformed state.

Adrenalectomy↗
PubMed1985

Evolution of cell types and T-cell subsets in the spleens of Mycobacterium bovis BCG-resistant and M. bovis BCG-susceptible strains of mice after infection with M. bovis BCG.

In mice, the early host response to intravenous infection with small doses of dispersed Mycobacterium bovis BCG is controlled by the Bcg gene. After infection with a low dose of M. bovis BCG, Lyt-1+ cells were generated in the spleens of BCG-susceptible mice (Bcgs) in parallel with an increase in the proportion of phagocytic cells. Very few changes occurred in the splenic cell types of BCG-resistant mice (Bcgr).

Animals↗
PubMed1985

Visual imagery and the use of mental practice in the development of motor skills.

This paper provides a critical review of research on mental practice, with special emphasis on works investigating the role of visual imagery in this type of learning technique. Relevant properties of images and conditions required for their effectiveness in mental practice of motor skills are analyzed in the light of empirical evidence. The paper examines the specific question of individual imagery differences in mental practice research. Finally, implications for future research are discussed as regards the impact of certain kinds of physical training on mental imagery.

Cognition↗
PubMed1984

A near-infrared investigation of cytochrome c oxidase in higher plant mitochondria.

Optical features of cytochrome c oxidase in potato mitochondria have been characterized in the near-ir region. In order to discriminate the respective properties of the various redox centers, the redox state was monitored from free and inhibited, bound species. Appropriate comparisons singled out difference spectra which can be attributed specifically to CuA and CuB. The CuA difference spectrum (red-ox) exhibits a negative band centered at 812 nm and, analogous to its mammalian counterpart, the so-called 830-nm band (delta epsilon red/ox = -2.0 mM-1 cm-1). The unusual difference spectrum (red-ox) assigned to CuB is characterized by a broad positive band also centered at 812 nm with an extinction coefficient of delta epsilon red/ox = 4.3 mM-1 cm-1.

Binding Sites↗
PubMed1984

Influence of molybdate, ionic strength and pH on ligand binding to the glucocorticoid receptor.

The addition of molybdate to rabbit liver cytosol increased significantly the affinity of the glucocorticoid receptor for [3H] dexamethasone without influencing the concentration of binding sites. This effect was concentration dependent. Analysis of the binding data by curve-fitting and Scatchard plot revealed the occurrence of a complex binding process in the presence of molybdate. The pH-dependence curve of the binding was shifted towards alkaline values by the oxyanion. Taken together, these data suggest that molybdate exerts its effects via an interaction with the receptor molecule.

Animals↗
PubMed1983

[Strategy of the use of immunological tests in the topographical diagnosis of urinary infections].

Assays for bacteria-specific antibodies were performed in 423 hospital patients with urinary tract infection (UTI), 184 of whom also had serodiagnosis by passive haemoagglutination with the strain responsible for the infection. The results of serodiagnosis were expressed as the difference in dilution between the antibody titres found in the patients and those found in pooled sera from healthy subjects. On the basis of this study, a rationale for immunological investigations, particularly in adults, is suggested. When bacteria-specific antibodies are lacking the probability of a lower UTI is 98%; when they are present, the probability of an upper UTI is only 74.5%, but the figure rises to 95% with a positive passive haemoagglutination serodiagnosis. In patients with negative serodiagnosis and positive bacteria-specific antibodies, a topographical diagnosis of UTI by immunological methods becomes impossible. In children, these methods are of little use owing to their poor sensitivity in detecting bacteria-specific antibodies, but the information provided by serodiagnosis is useful for determining the site of infection.

Adolescent↗
PubMed1982

Dynamics of carbon monoxide recombination to fully reduced cytochrome c oxidase in plant mitochondria after low-temperature flash photolysis.

Rebinding of CO to reduced cytochrome c oxidase in plant mitochondria has been monitored optically at 590-630 nm after flash photolysis at low temperature from 160 to 200 K. (1) Under 100%-CO saturation, CO rebinding exhibits a four-step mechanism. The thermodynamic parameters of the first phase have been determined; its activation energy, Ea1, is 38.9 kJ.mol-1 and its enthalpy, delta H+/-1, and entropy, delta S+/-1, of activation are respectively 37.5 kJ.mol-1 and -75.8J.mol-1.K-1. (2) When the CO concentration is decreased to 0.2%, rebinding still occurs according to a four-step mechanism. The rate constant of the first phase is CO-concentration-independent. Under non-saturating conditions there is only one CO molecule per occupied site. The rebinding mechanism does not require additional CO molecules to be present in the haem pocket. (3) Dual-wavelength scanning experiments failed to detect optical forms correlated with the resolved phases. (4) Results are discussed with respect to previous work related to CO rebinding to mammalian cytochrome c oxidase and myoglobin.

Binding Sites↗
PubMed1981

Resolution of two compound C-type intermediates in the reaction with oxygen of mixed-valence state membrane-bound cytochrome oxidase.

The reaction of mixed-valence state membrane-bound cytochrome oxidase with oxygen has been studied by difference spectroscopy with reference to the unliganded state and by the low temperature technique of Chance and coworkers. Three intermediates, compound A2 and two compound C-type components denoted C606 and C610, have been resolved in time and wavelength in the alpha region. Their optical properties are defined in the visible range. Compound A2 disappearance and compound C606 formation exhibit first-order kinetics with identical rate constants: 2.4 . 10(-3) s-1 at -94 degrees C. Compound A2 has its alpha band maximum at 590 nm and shares an isosbestic point at 595 nm with the C606 species. The alpha band of this intermediate peaks at 606 nm. Compound C610 is the real end point of the reaction and its alpha band maximum appears at 610 nm. Compound C606 is interpreted as resulting from the transfer of one electron from heme alpha 3 copper to oxygen and compound C610 as expressing a molecular reorganization due to the effect of the temperature. Structural requirements for the location of CuB in the active site are discussed. It is concluded that the three observed compounds are the only intermediates formed in the reaction between oxygen and mixed-valence state membrane-bound cytochrome oxidase.

Animals↗
PubMed1981

Reaction of Mixed Valence State Cytochrome Oxidase with Oxygen in Plant Mitochondria: A STUDY BY LOW TEMPERATURE FLASH PHOTOLYSIS AND RAPID WAVELENGTH SCANNING OPTICAL SPECTROMETRY.

The reaction of mixed valence state cytochrome oxidase (Cu(A) (2+)a(3+) . Cu(B) (+)a(3) (2+)) with O(2) at 173 K has been investigated in purified potato mitochondria by low temperature flash photolysis and rad wavelength scanning optical spectrometry in the visible region. The kinetics of the reaction have been analyzed simultaneously at six wavelength pairs (586-630, 590-630, 594-630, 604-630, 607-630, and 610-630 nanometers) by nonlinear optimization techniques, and found to proceed by a two-species sequential mechanism. The "pure" difference spectra of the two species, I(M) and II(M), relative to unliganded mixed valence state cytochrome oxidase have been obtained. The difference spectrum of species I(M) is characterized by a peak at 591 nanometers, with a shoulder at 584 nanometers and a trough at 602 nanometers, and that of species II(M) by an alpha band split into a prominent peak at 607 nanometers and a small side peak at 594 nanometers. Evidence is presented to suggest that these two bands arise from O(2) (-) --> Cu(B) (2+) and O(2) (-) --> a(3) (2+) charge transfer transitions which would imply that O(2) (-) forms a bridging ligand between Cu(B) and the iron atom of cytochrome a(3) in species II(M). The kinetics of the reaction and the spectral characteristics of species I(M) and II(M) obtained with the potato mitochondrial system are compared and contrasted with data in the literature on the beef heart mitochondrial system.

Journal Article↗
PubMed1981

Optical and Potentiometric Study of the b- and c-Type Cytochromes in Mushroom Agaricus bisporus Lge Mitochondria.

Differential spectrometry revealed two species for the b-type, as well as for the c-type, cytochromes in mitochondria from Agaricus bisporus Lge. The two b-type components are denoted according to their peak position in the alpha region at room temperature, i.e. b(560) and b(566). The b(556) component present in all the studied higher plant mitochondria was not detected in the system. At 293 K, the c-type cytochromes exhibit a common alpha band with a maximum at 550 nanometers. This band is split at 77 K, with peak positions at 547 nanometers (cytochrome c) and 552 nanometers (cytochrome c(1)).Redox titrations, analyzed according to a new method (Denis, Neau, Blein 1980 Bioelectrochem Bioenerg 7: 757-773), also yielded the resolution of two species of b-type and c-type cytochromes. The b components have midpoint potential values at pH 7.2 and 20 C of E(m1) = 40 +/- 10 millivolts and E(m2) = 175 +/- 10 millivolts. Their calculated individual difference spectra exhibit alpha bands with identical maxima at 561 nanometers, in contrast with optical observations. The midpoint potential values of the resolved c components are 210 +/- 10 millivolts and 292 +/- 5 millivolts at pH 7.2 and 20 C. Their corresponding calculated difference spectra have their alpha band maxima at 553 and 551 nanometers. These two species have been identified respectively with cytochrome c(1) and cytochrome c. The ratio of the maximum optical contributions, c/c(1), is in the range 4/1 to 5/1, in contrast with other results related to yeast or higher plant mitochondria where it amounts to 2/1 or even 1.3/1.

Journal Article↗