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Biomedical subjects

H Michel

Publications and source records attributed to H Michel.

At least 325 records · Page 18Linked to original sources
PubMed1982

Characterization and crystal packing of three-dimensional bacteriorhodopsin crystals.

The three-dimensional crystals of the integral membrane protein bacteriorhodopsin have been characterized by X-ray diffraction and freeze-fracture electron microscopy: the needle-like form A crystals belong to space group P 1 (pseudohexagonal) with seven molecules per crystallographic unit cell forming one turn of a non-crystallographic helix. The probable arrangement of the bacteriorhodopsin molecules is derived from freeze-fracture electron micrographs and chromophore orientation. Membrane-like structures are not present. The same helices of bacteriorhodopsin molecules found in crystal form A also make up the cube-like crystal form B. They are now arranged in all three mutually perpendicular directions. These cubes are always highly disordered, since the unit cell length corresponds to 6.7 molecules of the 7-fold helix. Very often, conversion of bacteriorhodopsin from the three-dimensional crystals into filamentous material occurs.

Journal Article↗
PubMed1982

Halobacterium halobium phage øH.

Phage øH, a novel virus of the archaebacterium Halobacterium halobium, resembles in size and morphology two other Halobacterium phages. One-step growth curves show a 5.5 h eclipse, a latent period of 7 h, and an apparent burst size of 170. Phage øH contains linear, double-stranded DNA which has a molecular weight of 39 x 10 and a GC content of 65%. A packaging model accounting for the partial circular permutation and terminal redundancy of øH DNA is suggested. Partial homology of øH DNA with the DNA of H. halobium, predominantly with the AT-rich satellite DNA, was observed. The presence of minor restriction fragments of øH DNA which could be removed by purification of phage from single plaques suggests the existence of phage variants with rearranged DNA. A strain of H. halobium containing øH DNA was isolated which is resistant to infection by phage øH.

Journal Article↗
PubMed1982

On the environment and the rotational motion of amphiphilic flavins in artificial membrane vesicles as studied by electron paramagnetic resonance spectrometry.

This paper continues the studies of vesicle-bound flavins ('anisotropic flavin chemistry'). It is possible to anchor the flavin nucleus in various modes within the lipids/water interface by means of long aliphatic chains and using different saturated lipids, thereby mimicking the specific binding of the coenzyme to the apoprotein in flavoproteins. Based on absorption spectroscopy and EPR spectroscopy studies we explored the rotational mobility and the microenvironment of membrane-bound amphiflavin radicals. N(5)-unsubstituted amphiflavin radicals exhibit a similarly high disproportionation constant as known from isotropic flavin chemistry. However, reasonable stabilization of the radical was achieved by introduction of an alkyl group in position 5 in the reduced state prior to the one-electron oxidation. Adopting the fine structure of the corresponding EPR spectra as assay for the mobility of the semiquinone, we determined rotational relaxation times ranging from 60 ns in the crystalline state down to 10 or 15 ns in the liquid-crystalline state of the membrane. The solvatochromic effect shown by absorption spectra of the membrane-bound flavin radicals reflects a dielectric constant of the microenvironment of c = 30-40, corresponding to the lipid/water interface region. The results obtained in this study are consistent with those obtained previously, from fluorescence analyses, supporting our former conclusions.

Flavins↗
PubMed1982

Palliative endoscopic treatment of malignant esophageal stenosis using a Häring prosthesis.

The aim of this work was to analyze the outcome of 78 cases of esophageal cancer for which the endoscopic placement of a Häring prosthesis was chosen as a palliative method of treatment. The average length of hospitalization was 10 days and the average survival time was 90.8 days. The postinsertion mortality rate was 6% and there were 44 complications. The best indications are carcinoma of the lower two thirds of the esophagus, neoplastic mediastinitis and esophageal fistulae.

Esophageal Neoplasms↗
PubMed1981

[24 hour polygraphic study of the waking-up and falling asleep periods in patients with hepatic encephalopathy (author's transl)].

24 h sleep-waking EEG records of 23 patients with hepatic cirrhosis, 18 having hepatic encephalopathy, were studied. Comparison with a group of normal controls showed an increase in diurnal somnolence (08 h-22 h) and nocturnal waking (22 h-08 h) in all the patients. There was a significant reduction in the longest duration of waking and uninterrupted sleep periods in the patients with cirrhosis. Triphasic waves (characteristic of hepatic encephalopathy) were usually increased during waking and reduced in sleep. The factors involved in this disturbance of sleep-waking patterns in hepatic encephalopathy are discussed (cerebral monoamines, false neurotransmitters, cerebral arteriovenous shunts...).

Circadian Rhythm↗
PubMed1981

[Comparative hepatic toxicity of perhexiline maleate and griseofulvin in mice].

Hepatic toxicity was observed in mice which had received Griseofulvin or Perhexilin Maleate over a period of several months. Treatment of griseofulvin alone gave rise to hepatitis with the presence of Mallory bodies (MB) whereas the same length of treatment with Perhexilin Maleate was associated with steatonecrosis with an absence of MB. When treatment was followed by a one month rest period hepatic lesions disappeared with no trace of sequelae. Cross-treatment studies showed that one week of Perhexiline Maleate was sufficient to induce MB in mice pretreated with Griseofulvin. Similarly, Griseofulvin administered to mice pretreated with Perhexilin Maleate gave rise to MB formation after one week as opposed to the usual two months incubation time (DENK et al.). The histological nature and mode of formation of these MB was identical to that encountered in acute alcoholic hepatitis. On addition, combined drug therapy employing Perhexilin Maleate suggests a particular hepatic toxicity in man in cases where the liver has become predisposed due to other therapeutic.

Animals↗
PubMed1980

[Amineptine-induced cholestatic hepatitis. 5 cases (author's transl)].

The authors have observed 5 cases of cholestatic jaundice with cytolysis during treatment with amineptine, a new tricyclic compound recently made available. The responsibility of the drug was virtually certain for the following reasons: (a) there was no other cause of jaundice, such as viral infection, gallstones, toxic agents or association with other hepatotoxic drugs; (b) clinical and biochemical findings were similar in all patients; (c) in 2 patients, reintroduction of the drug after temporary withdrawal resulted in rapid recurrence of the condition, with the same symptoms and course. The shorter delay (2 and 8 days instead of 11 and 18 days) between absorption of amineptine and reappearance of the symptoms in these two patients is suggestive of an immunoallergic mechanism.

Adult↗