Molecular clues to pathogenesis in prion diseases.

The infectious agent of the transmissible spongiform encephalopathies (TSE) resembles a virus in that it propagates in vivo and has distinct strains. However, compelling evidence strongly suggests that a posttranslational structural alteration in a glycoprotein PrPC (the normal, cellular isoform of the so-called prion protein) is responsible for pathogenesis of these diseases. According to this hypothesis-now close to being generally accepted-iatrogen, sporadic and familial forms of TSE would have the same molecular mechanism: the conversion of PrPC into a protease-resistant isoform PrPSc kinetically behaves as an autocatalytic process which, combined with the high turnover rate of the normal isoform, may endow the system with bistability properties and subsequent threshold behavior between normal and pathogenic steady-states.

Power and limits of laser scanning confocal microscopy.

In confocal microscopy, the object is illuminated and observed so as to rid the resulting image of the light from out-of-focus planes. Imaging may be performed in the reflective or in the fluorescence mode. Confocal microscopy allows accurate and non-destructive optical sectioning in a plane perpendicular or parallel to the optical axis of the microscope.

[Quantitative histo-enzymological study of delta 5-3 beta-hydroxysteroid dehydrogenase activity in rat testis during the perinatal period. Relation with testicular crisis in the newborn rat].

The purpose of the present work was to determine if the neonatal testosterone surge in the rat (between 0 and 6 h after birth) was coincident with the histological and histochemical changes in the neonatal period. The histological study shows a decrease in the number of gonocytes and cells in mitosis. These observations are in good agreement with the results obtained by other authors.

Aggregation and proton release of purple and white membranes following cleavage of the carboxyl-terminal tail of bacteriorhodopsin.

Our results indicate that the previously reported decrease in proton release by proteolyzed purple membrane sheets was due merely to the aggregation state of these preparations and not to the loss of the carboxyl-terminal tail. Changes in H+/M412 ratios obtained for purple and white membrane preparations correlate with the measured aggregation. White membrane preparations consistently exhibit H+/M412 ratios more than twice those measured for native purple membranes under the same conditions.

Study of the electrokinetic properties of reconstituted sarcoplasmic reticulum vesicles.

A study of electrokinetic properties of reconstituted sarcoplasmic reticulum was undertaken to determine the nature of the groups bearing the negative charge of the membrane. After incorporation of phosphatidylcholine into the bilayer, it was found that the Ca2+-ATPase embedded in functional vesicles bore 3e- per mole. When the surface charge density of the hydrodynamic particles became more negatively charged by incorporation of phosphatidylserine molecules, the reconstituted vesicles had a tendency to build large structures resulting from vesicle-vesicle interaction and containing large amounts of divalent cations.