Studies on the quaternary structure of the first enzyme for histidine biosynthesis

Resumen Se han realizado estudios de asociación-disociación por filtración en gel con el primer enzima de la biosíntesis de histidina enEscherichia coli, en presencia de sustratos y ligandos. Se observa una interconversión reversible entre las formas dímero, tetrámero y exámero, y una agregación irreversible de orden superior.     

Calcium ion binding to blood cell surfaces

Zusammenfassung Neue Erkenntnisse über die quantitativen Zusammenhänge von fixierten, negativen Ladungen an Zellmembranen und ihren Interaktionen mit Kalzium-Ionen. Die elektrophoretische Analyse der Bindung von Ca-Ionen an menschliche polymorphkernige Leukozyten und rote Blutkörperchen deutet die Anwesenheit von mindestens 3 verschiedenen anionischen Ladungskonfigurationen in der peripheren Zone der Zellen an. Die zwischen den Ca-Ionen und den Oberflächen-Anionen existierenden elektrochemischen freien Bindungsenergien sind relativ schwach; daraus folgert, dass die Ca-Ionen nur schlechte Komponenten für eine direkte interzelluläre überbrückung darstellen.     

The binary progenitor of Tycho Brahe's 1572 supernova

The brightness of type Ia supernovae, and their homogeneity as a class, makes them powerful tools in cosmology, yet little is known about the progenitor systems of these explosions. They are thought to arise when a white dwarf accretes matter from a companion star, is compressed and undergoes a thermonuclear explosion. Unless the companion star is another white dwarf (in which case it should be destroyed by the mass-transfer process itself), it should survive and show distinguishing properties. Tycho's supernova is one of only two type Ia supernovae observed in our Galaxy, and so provides an opportunity to address observationally the identification of the surviving companion. Here we report a survey of the central region of its remnant, around the position of the explosion, which excludes red giants as the mass donor of the exploding white dwarf. We found a type G0-G2 star, similar to our Sun in surface temperature and luminosity (but lower surface gravity), moving at more than three times the mean velocity of the stars at that distance, which appears to be the surviving companion of the supernova.