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Biomedical subjects

M Joniau

Publications and source records attributed to M Joniau.

At least 55 records · Page 3Linked to original sources
PubMed1982

An intramolecular excimer forming probe used to study the interaction of alpha-lactalbumin with model membranes.

The nonconjugated bichromophoric molecule 1,3-di(1-pyrenyl)propane shows, besides the pyrene monomer fluorescence, a structureless emission due to an intramolecular excited dimer (excimer). In the case of intramolecular excimer forming systems, the ratio of the emission intensities of excimer vs. monomer (IE/IM) is sensitive to changes in membrane structure as will be illustrated here. The present molecule is a useful probe to report on lipid-protein interactions, at least in our model system. We have introduced it into the hydrocarbon layer of dimyristoylphosphatidylcholine vesicles in order to study their interaction with alpha-lactalbumin (alpha-LA) as a function of pH and temperature. On the basis of steady-state fluorescence, kinetic, and energy transfer studies, we have found that, at pH 4, alpha-LA strongly interacts with the lipid bilayer. In steady-state fluorescence experiments, changes of the ratio IE/IM and shifts of the transition temperature have been observed, reflecting changes of membrane structure caused by interaction with alpha-LA. Kinetic studies of the rate of interaction of alpha-lactalbumin and measurements of energy transfer from excited tryptophan(s) to the fluorescent probe confirm the steady-state experiments. Our results agree with previously reported microcalorimetric, gel chromatographic, and fluorescence polarization studies.

Animals↗
PubMed1981

Nucleated assembly of mitotic microtubules in living PTK2 cells after release from nocodazole treatment.

The reassembly of microtubules is described in mitotic cells after release from nocodazole-induced block. The formation of microtubules was followed by light microscopic immunocytochemical staining using the PAP method, combined with toluidine blue staining of the chromatin. The light microscopic observations on whole cells were compared with ultrastructural observations on thin sections. This step is essential to ascertain complete destruction of microtubules during the nocodazole treatment and to correlate immunocytochemical staining with the presence of microtubules. Removal of nocodazole (10 or 1 micrograms/ml) after a sufficiently long incubation to induce a complete disappearance of microtubules resulted in the appearance of tubulin staining specifically associated with the centromeres and with one or two isolated points in the cytoplasm. Electron microscopy confirmed that the staining was due to the massive accumulation of small microtubules at the kinetochores and centrosomes. Kinetochore nucleation was seen only in association with condensed metaphase-stage chromosomes and not with the less-condensed prophase chromosomes. In a second type of experiment cells were allowed to enter mitosis in the presence of an incompletely active concentration of nocodazole (0.1 microgram/ml). The construction of the mitotic spindle was arrested; however, short microtubules were assembled at the kinetochores and centrosomes. These experiments demonstrate that in living mitotic PTK2 cells the kinetochores, as well as the centrosomes, exert a nucleating action on tubulin assembly. The further elongation of microtubules after removal of nocodazole was seen to occur preferentially along axes between the centrosomes and the kinetochores. This resulted in the construction of normal metaphases that evolved through anaphase and telophase. We have attempted to formulate a hypothesis that may explain the oriented assembly that seems to be essential in the construction of the spindle.

Animals↗
PubMed1980

Behavior of beef-heart cytochrome c oxidase in reconstituted proteovesicles. A systemtic evaluation of the influence of phospholipid polar headgroup and fatty-acyl side chains.

1. Phospholipid-depleted cytochrome c oxidase is incorporated in vesicles, built up of phospholipids of known polar headgroup and fatty-acyl side chains. 2. Maximal reactivation is obtained only when the fatty-acyl side chains provide a fluid environment. 3. Fluid zwitterionic phospholipids are found to be more efficient reactivators than fluid anionic ones. 4. Irrespective of the polar headgroup type, two narrow ranges of activation energies for the enzymatic reaction are calculated from the Arrhenius plots: 81--92 kJ/mol in solid and 51--61 kJ/mol in fluid conditions. 5. Cytochrome c oxidase is also incorporated in a series of vesicles, each built up of an equimolar amount of two phospholipids which differ in their polar headgroup type and/or their fatty-acyl side chain characteristics. From the localization of the enzyme activity profiles, obtained with these mixtures, tentative deductions are made about the preference of cytochrome c oxidase for different phospholipid molecules.

Animals↗
PubMed1978

Evidence for unaltered structure and in vivo assembly of microtubules in transformed cells.

By using immunoperoxidase cytochemistry at the light and electron microscopic level, microtubles were visualized in a number of "normal" nontumorigenic and transformed tumorigenic cell lines. A well-defined cytoplasmic microtubule complex exists in both normal and transformed interphase cells. The distribution of this complex closely correlates with the cell shape and the degree of cell spreading. Our data support the idea that these properties determine the pattern of the cytoplasmic microtubule complex, rather than the reverse. Ultrastructural observations of immunoperoxidase-stained tumor cells showed characteristic microtubules in cells in which the microtubules were poorly resolved at the light microscopic level. The results suggest that microtubule assembly and structure are unaltered in transformed cells. However, this conclusion does not exclude the possibility that some of the microtubules' functions might be impaired in a yet-unknown way.

Cell Line↗
PubMed1977

Ultrastructural immunocytochemical distribution of tubulin in cultured cells treated with microtubule inhibitors.

Microtubules in tissue cultured cells are stained immunocytochemically with the PAP-method using a purified antitubulin antibody. Treatment of the cells with microtubule inhibitors (colchicine, nocodazole, vinblastine) results in the disappearance of microtubules. The diffuse cytoplasmic staining is strongly increased in the cells by colchicine and nocodazole. Vinblastine produces paracrystalline aggregates that are strongly stained and macrotubules that are unstained. The diffuse staining is much less in vinblastine-treated cells. The bundles of intermediate filaments that are induced by all microtubule inhibitors do not bind the antitubulin antibody.

Benzimidazoles↗