Acta biochimica et biophysica; Academiae Scientiarum Hungaricae最新文献

Cytosol glucocorticoid receptors of five different lymphoid tissues of chicken and rats were characterized and compared by physicochemical parameters. Binding specificity of receptors was found to be similar, except that cytosol receptors of chick tissues appeared slightly more specific for dexamethasone than those from rats. Association rate constants of the dexamethasone-receptor complex were higher by about one order of magnitude in the case of chicken thymus and bursa than in other cytosols. Dissociation of dexamethasone-receptor complex occurred in one step in rat tissues, whereas in case of chicken tissues two phases of dissociation were discernible. Differences between Ka and the ratio of the association and dissociation rate constants are explained by non-equilibrium conditions. The stability of receptors from the two species differed significantly, the chick receptor being more stable. Hormone-receptor complex from each tissue could be separated into two fractions by DE-52 chromatography. The peak eluted at the lower KCl concentration in the case of chick corresponded to the fast dissociating hormone-receptor complex. Kinetic analyses proved to be just as useful as ion-exchange chromatography for the characterization of, and distinguishing between, glucocorticoid receptors.

Control and acute leukemic cells of AKR:Lac C3H mg:Lac/F1 hybride mice were labeled either with ethidium bromide or ethidium bromide plus fluorescamine. Theoretical and experimental evidence shows that the ethidium bromide binding ability of cells and the average efficiency of Förster-type fluorescence energy transfer between fluorescamine and ethidium bromide inside the cells depend on both the cell and dye concentrations. It is shown further that fluorescamine treatment enhances the uptake of ethidium bromide by both normal and leukemic cells. A sevenfold difference was found in ethidium bromide binding ability between normal and leukemic cells at optimal dye concentration.

Zn2+, Fe2+, Cu2+, Ca2+, and Mg2+ were determined by means of atomic absorption techniques in tetramethylammonium hydroxide digests of cell organelles isolated from normal rat liver tissue. The metal content of the cell organelles was expressed with reference to their protein content. The results showed that digestion with tetramethy la ammonium hydroxide can be applied for the determination of metal to protein ratios in the cell organelles and that these ratios appear to be suitable for the characterization of cell organelles.

UV photoproducts were induced in two types of uracil solid phase systems: in evaporated and recrystallized thin layers and in dried aquaeous solution respectively. The nature of the photochemical reactions in the two systems was compared by gradient elution column chromatography. In the case of dried solution two types of cyclobutane dimers were isolated, but in recrystallized thin layers only one type was found. The efficiency of the reaction in evaporated layers was much higher than in those produced by drying. Based on the crystal structure of uracil and previous absorption spectroscopic studies of the photochemistry of thin crystalline layers it was stated, that the single type of photodimers produced in evaporated thin layers is characteristic for the photochemical reaction proceeding in crystal matrix; and its structure was proposed to be identical with that of the cis-syn stereoisomer dimer.

Heat inactivation of porcine kidney aminoacylase (E.C.3.5.1.14) was investigated under different conditions i.e. at different temperatures, protein concentrations and pH values). Kinetic analysis of the inactivation process suggests that aminoacylase is a dissociable enzyme: the dimeric form is dissociated to enzymatically active monomers and the heat stability of the dimer is higher than that of the monomers. High temperatures, dilution and pH values other than neutral, all promote dissociation. The KDapp at 60 degrees C, pH 7.0 is of the order of 10(-6) M.

K-rich solution, the isotony of which corresponds to normal Ringer's solution, was used in our experiments: 4.59 g KCl + 40.5 g saccharose, 1000 ml bidistilled water. Freshly prepared living muscles of Rana esculenta (m. sartorius, m. iliofibularis, m. peroneus, m. tibialis, m. gastrocnemius, m. semimembranosus) got into K-contracture in this solution, but they relaxed within some minutes. In muscles of dead frog (which canno tbe stimulated with 110 V a.c.) the K-rich solution did not elicit contracture, i.e. on the one hand K-contracture could be observed only in living muscle and on the other hand, the muscles did not lose their excitability after the K-contracture had ceased (a.c. 2V).