Physiological chemistry and physics最新文献

It has been postulated that high concentrations of parathyroid hormone might increase transport of amino acids across basal lateral membrane into the cell and that the amino-aciduria seen in hyperparathyroidism occurs because of leakage across brush border membrane into the lumen. Accordingly, we separated plasma membranes from renal proximal convoluted tubules into basal lateral and brush border fractions, both of which form vesicles. We found that for the vesicles from rabbits pretreated with parathyroid hormone, 14C-L-alanine incorporation was indeed enhanced in the basal lateral fraction, but not in the brush border fraction. Nor was significant enhancement found for vesicles from rabbits pretreated with cycloheximide in addition to hormone. We conclude that L-alanine uptake is greatest in the basal lateral membrane fraction after parathyroid hormone treatment in vivo. In such case, the two membranes also differ from each other in endocrine response.

Some organic dyes of a double diazo structure, pressurized into thin films, show trapping of magnetic flux at room temperature, suggestive of the behavior of type 2 superconductors. Some also show switching from low to high electrical conductivity at a voltage threshold, like amorphous inorganic semiconductors. An applied magnetic field facilitates switching, as well as current flow after switching, in a dye that traps magnetic flux but not in a dye of almost similar structure that does not trap magnetic flux. For best results, the magnetic field should be applied before switching and in a direction perpendicular to current flow. The magnetic field effects observed in the dye films at room temperature may be analogous to "anomolous" magnetic phenomena observed in metallic superconductors and/or in superconducting Josephson junctions at low temperatures. The implied possibility of superconductive mechanisms of biomagnetic effects, and apparent relation to the electrical switching seen in wet melanin, give the findings biological relevance.

Swelling of crab claw nerve fibers, monitored as weight increase, takes place while the nerve fibers are immersed in a medium high in K+, Cs+ or Rb+ concentration, or in artificial seawater to which 0.2 mM veratridine is added. Similar swelling is observed in nerves in sodium salt solutions which also contain low concentrations of divalent cations. The swelling observed under these conditions is dependent on anions, giving a series (from efficient anion to less efficient ones): I- greater than SCN- greater than Br- greater than Cl- much greater than F- greater than glutamate, ethylsulfate. The presence of this series indicates that the nerve swelling observed is attributed to influx of external salt. Uptake measurements of radioactive anions and cations corroborate the presence of salt influx under these conditions. In analyzing the anion dependence of nerve swelling, two factors, membrane and cytoskeletal structure, are examined. It is shown that the cytoskeletal structure, which is sensitive to the lyotropic series of anions, plays an important role in this phenomenon.

Purified yeast nuclei contain proteolytic activities which are associated with chromatin. pH optimum is in the range 8.0--8.5. Partial purification reveals the presence of three fractions corresponding to different molecular weights. Boiled chromatin supernatants are able to inhibit proteolytic activity. The inhibition effect of various compounds is also described. The purity of the chromatin preparation seems to rule out artifacts due to contamination.

Binding of lectins to microbial cell walls was investigated by fluorimetric titration and Scatchard plot. Data were correlated with agglutinability. Concanavalin A and lectins of wheat germ, soybean, pea, lentil, and peanut were tested against Escherichia coli. Micrococcus luteus, Lactobacillus plantarum, and Bacillus subtilis. In cases where binding occurred, it was either nonspecific or positively cooperative. Agglutination was observed only in those combinations of lectin and microorganism that showed positive cooperative binding, suggesting a definite relation between binding and agglutination. Lectins binding to the same carbohydrate did not necessarily bind to the same microorganism, confirming the complexity of the lectin-receptor bond.

Monolayer cultures of 3T3 and WI-38 fibroblasts were pulse labeled with radioactive leucine in the presence of cycloheximide. The rate of protein degradation was measured and compared with that of SV-40 virus transformed cells. The results clearly show that normal and transformed cells have essentially identical rates of degradation of proteins synthesized in the presence of cycloheximide. These findings indicate that the lower rates of protein degradation observed in some transformed cells is not a general rule.

A model system of gaseous electron mobility, excitation, and plasma activity was used to study direct effects of six gases, including four general anesthetics, in oxygen. Helium increased, and nitrogen had minimal effects on gaseous excitation. Nitrous oxide, as well as the potent anesthetics halothane, enflurane, and isoflurane, inhibited gaseous excitation, nitrous oxide having the weakest anesthetic effect. The data are compatible with the view that anesthetic inhibition is mediated by Van der Waals dipole dispersion interactions among anesthetic molecules (e.g., halogenated hydrocarbons) and electrons accelerated by the applied field. Dipole dispersion interactions may also mediate anesthetic effects on synaptic protein conformational control.