Effect of ions on phospholipid layer structure as indicated by Raman spectroscopy.

Various anions and cations are found to induce changes in the layered structure of phosphatidylcholine-water systems as indicated by Raman Spectroscopy. From the ratio of Raman intensities, I1064/I1089, it is inferred that dipositive ions decrease the proportion of gauche character in the hydrocarbon chains, with the relative influence being: Ba2+ less than Mg2+ less than Ca2+ similar to Cd2+. Unipositive ions (Li+, K+ and Na+) produce no observed changes in the Raman spectrum of the lecithin dispersion. The proportion of gauche character of the hydrocarbon chains is found to be nearly independent of the anion for: Br-, Cl-, acetate-, I-, ClO4-, CNS- and SO42-. Dispersions prepared with a solution of KI+I2 produced Raman spectra in which the 1089cm-1 peak, which is characteristic of random lipid chains, was greatly intensified, presumably because of the presence of I3- which is known to penetrate the lipid lamellae. The observed trends are discussed.     

Cell-to-cell adhesion of dissociated embryonic brain cells; the effects of metabolic inhibitors and temperature

Brain cells from 16 to 18-day-old mice embryos were dissociated by mild trypsinization and rotated for 120 min. The area and density of of the adhesive complexes formed were registered using the method described previously. The adhesiveness of dissociated embryonic brain cells (measured during the 120 min of rotation) was diminished in the presence of inhibitors of protein synthesis (puromycin, cycloheximide and inhibition of mRNA synthesis actinomycin D). The inhibition was, however, not distinct, because 1 microgram/ml of cycloheximide and actinomycin was without any significant effect, and the degree of inhibition evoked by 10 micrograms/ml and 25 micrograms/ml of puromycin bordered on significance. However, protein synthesis inhibitors in long-term aggregation experiments had a pronounced inhibitory effect and/or induced destruction of the aggregates. Metabolic inhibitors (KCN and NaN3) caused an inhibition at the lowest level of significance (p less than 0.05) 10(-3) mol/l KCN reduced the final adhesive product significantly. Cells rotated at room temperature and at +5 degrees C adhere to the same extent as in control experiments (37 degrees C). The adhesion was significantly inhibited at +60 degrees C and also after freezing at -80 degrees C with subsequent thawing. The adhesion of cells exposed for 30 min to between +80 degrees C and 100 degrees C was completely abolished. The process of embryonic brain cell adhesion requires a low energy supply, and is relatively independent of biosynthetic processes and of temperature changes between +5 degrees C and +50 degrees C.     

Glycosaminoglycans of the plasma membranes of renal tubule and liver cells

Glycosaminoglycans were isolated from plasma membranes of hepatic and renal tubule cells of guinea pig. Plasmalemma of renal tubule cells contained more total glycosaminoglycans, hyaluronic acid, chondroitin-4 sulfates and chondroitin-6 sulfates, and less dermatan sulfates and heparin sulfates than liver plasma membranes. These glycocalyx components, owing to their polyanionic properties, may have a role in the transport of water, ions, and macromolecules across the cell membrane.     

Specific [3H] Glutamate Binding in the Cerebral Cortex and Hippocampus of Rats During Development: Effect of Homocysteine-Induced Seizures

Specific [³H]glutamate binding to synaptic membranes from the cerebral cortex and hippocampus of 7-, 12- and 18-day-old rats was examined, both in control animals and during seizures induced by homocysteine. In the cerebral cortex a transient peak of glutamate binding was observed in 7-day-old group, whereas in the hippocampus it occurred in 12-day-old animals. Total specific [³H]glutamate binding was not influenced by preceding seizure activity in either of the age groups and both the studied regions. NMDA- and QA-sensitive glutamate bindings represent the highest portion of the total binding. Moreover, NMDA-sensitive binding in the cerebral cortex of 7-day-old rats is significantly higher as compared to the two more mature groups. The proportion of individual receptor subtypes on total binding in each age group was not influenced by preceding seizure activity. However, NMDA-sensitive binding in the hippocampus of 12-day-old rats, sacrificed during homocysteine-induced seizures, was significantly increased as compared to corresponding controls. In contrast to the effect of NMDA, AMPA, kainate and quisqualate which displaced to a different extent [³H]glutamate binding, homocysteine had no effect when added to membrane preparations. Similarly, [³H]CPP and [³H]AMPA bindings were not affected in the presence of homocysteine. It thus seems unlikely that homocysteine is an effective agonist for conventional ionotropic glutamate receptors. Its potential activity at some of the modulatory sites at the NMDA receptor channel complex or at metabotropic receptors has to be clarified in further experiments.     

The interrelation between elongation and IAA-1-14C metabolism in wheat coleoptile sections

It has been shown that intensive elongation of wheat coleoptile sections is correlated with indoleacetic acid-1-¹⁴C metabolism. In tissues actively growing the disappearance of indoleacetic acid-1-¹⁴C and formation of conjugates and metabolites (indoleacetamide, indoleacetyl-β-D-glucose, indoleacetyl aspartic acid) is twice as high as in sections where growth has been stopped by physical constraint (plaster) or in tissue which did not elongate by an unknown reason.     

Different cyclic AMP requirements for induction of the arabinose and lactose operons of Escherichia coli

Valyl-tRNA deprivation causes a threefold reduction of the polysome content of stringent cells but not of relaxed cells. The polysomes of valyl-tRNA-deprived stringent and relaxed cells decay in the presence of rifampin at a rate very similar to that observed in growing cells.Polysome assembly and decay were studied in valyl-tRNA-deprived stringent and relaxed strains after first causing the pre-existing polysomes to be converted to monosomes by glucose starvation. The capacity for polysome assembly is normal in relaxed cells and is reduced by a factor of three in stringent cells. The polysomes which reassemble in glucose-starved cells also decay in the presence of rifampin at a rate similar to that of the polysomes of growing cells. The polysomes which assemble in relaxed cells are potentially functionally competent, as shown by their ability to incorporate amino acids in an in vitro proteinsynthesizing system. Valyl-tRNA deprivation causes an intense shift in the polysome size distribution in stringent cells, but only a moderate shift in relaxed cells. A model for the control of the polysome level in amino acid-starved cells, based on these observations, is presented here.