Fusion of microsomal vesicles

Summary Studies which indicate the fusion of rat liver microsomal vesicles show that the rate of fusion of microsomal vesicles, as revealed by electron microscopic examinations, is dependent on the fusion temperature and the amount of detergent present in the microsomal suspension.Acknowledgments. We thank Miss R. Kannler for excellent technical assistance. The electron microscopy was performed in Anatomisches Institut and the Strahlenzentrum of the University of Giessen. This investigation was supported by the Deutsche Forschungsgemeinschaft (Schu 54/5) and by the Stiftung Volkswagenwerk (AZ 11 2454).     

Effets immédiats de quelques antibiotiques sur l'électro-osmose chezNitella flexilis L.

Summary The short term effects of chloramphenicol, polymyxin sulfate and oligomycin A + B (the latter in 0,5M alcoholic solution) on the basic flow and the electrosmosis inNitella were studied. Both chloramphenicol and polymyxin increase the basic flow but only polymyxin increases the electro-osmotic efficiency.     

Timescales of shock processes in chondritic and martian meteorites

The accretion of the terrestrial planets from asteroid collisions and the delivery to the Earth of martian and lunar meteorites has been modelled extensively. Meteorites that have experienced shock waves from such collisions can potentially be used to reveal the accretion process at different stages of evolution within the Solar System. Here we have determined the peak pressure experienced and the duration of impact in a chondrite and a martian meteorite, and have combined the data with impact scaling laws to infer the sizes of the impactors and the associated craters on the meteorite parent bodies. The duration of shock events is inferred from trace element distributions between coexisting high-pressure minerals in the shear melt veins of the meteorites. The shock duration and the associated sizes of the impactor are found to be much greater in the chondrite (approximately 1 s and 5 km, respectively) than in the martian meteorite (approximately 10 ms and 100 m). The latter result compares well with numerical modelling studies of cratering on Mars, and we suggest that martian meteorites with similar, recent ejection ages (10(5) to 10(7) years ago) may have originated from the same few square kilometres on Mars.     

Variations de la différence de potentiel électrochimique des chlorures chezNitella en présence de benzène sulphonate

Summary The chloride electrochemical potential difference between the inside of cells ofNitella translucens and some external solutions, where Cl has been progressively replaced by benzenesulphonate, has been measured by means of Ag-AgCl electrodes. It appears that benzenesulphonate moves into the cell by an electrogenic pump and that the uptake of Cl byNitella is not in contradiction with a carrier hypothesis.

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This work was supported by grants from the F.N.R.S. and was carried out in the Biophysics Section of the Edinburgh University. We are indebted to Dr. E. J.Williams and Dr.Hogg for having sponsored this research and kindly provided the material.     

Effect of the venom sac content of the oriental hornet (Vespa orientalis) on the metamorphosis of the toad tadpole (Bufo viridis)

Résumé Le venin de la guêpe (Vespa orientalis) supprime la métamorphose du têtard de crapaud (Bufo viridis) chez tous les animaux traités au stade prémétamorphique et chez 60% des animaux traités au stade prométamorphique. Onze des animaux traités ont montré un éclaircissement de la peau.     

Modification de la vitesse du courant cytoplasmique,induite à distance,par l'irradiation,chezNitella flexilis

Summary Irradiation of an internodal cell ofNitella flexilis induces in the adjacent internodal cell a transitory acceleration of cytoplasmic streaming; during 8 h at least the speed of this streaming is higher than in control internodal cells. It is probable that this phenomenon is due to transfer of certain substances from the irradiated cell.     

Beta 2-microglobulin restriction of antigen presentation.

Antigens are generally thought to be recognized by cytotoxic T lymphocytes as peptides in the context of class I major histocompatibility proteins complex, which are heterodimers of heavy chains noncovalently associated with beta 2-microglobulin (beta 2m). The highly polymorphic nature of the heavy chains and their resulting ability to present different sets of peptides has presumably evolved to allow potent immune responses against most pathogens. By contrast, the polymorphism of beta 2m is limited; seven alleles are known in the mouse and only one has been identified in humans. beta 2-Microglobulin was consequently thought to have only structural functions: namely, to ensure correct folding of class I molecules and their transport to the cell surface. Although beta 2m is not implicated directly in the formation of the peptide binding site, we report here that it participates in the selection of MHC class I molecule-associated peptides.