35Cl nuclear magnetic resonance studies of anion binding to halophilic proteins: Ferredoxin from Halobacterium of the Dead Sea

The anion-binding characteristics of ferredoxin from Halobacterium of the Dead Sea have been studied by ³⁵Cl^? NMR. It is found that the binding constant of Cl^? to halophilic ferredoxin is ca. 0.09 at 28 °C and that the binding enthalpy is positive. It is also found that the correlation time for chloride ions bound to halophilic ferredoxin is about 10 ns. The effect on the ³⁵Cl^?1 NMR signal of adding competing anions is also studied. Halophilic proteins like ferredoxin which have a high negative charge bind anions with low affinity but the ³⁵Cl^? quadrupole relaxation technique can conveniently monitor such weak binding.     

Inhibition of the predatory activity ofBdellovibrio by various environmental pollutants

The predatory activity of bdellovibrios is affected by various environmental pollutants such as detergents, heavy metals, and pesticides. This was shown in a two-membered system ofBdellovibrio andPhotobacterium, in which the effect of the predator on the bioluminescence of the prey indicated the activity of the former. The high sensitivity of the bdellovibrios toward certain chemicals (e.g., CdCl₂) indicates the possibility of using the system for biological monitoring of those chemicals.     

Bacteriorhodopsin in a bloom of halobacteria in the Dead Sea

A dense bloom of red halobacteria developed in the Dead Sea in the summer 1980, bacterial densities of up to 1.9 x10⁷ cells ml^-1 were observed. The population consisted of two types: pleomorphic, cup-shaped cells and rod-shaped cells. A high content of bacteriorhodopsin was found in the bloom (up to 0.4 nmol per mg protein). The rod-shaped Halobacterium was isolated and was shown to contain bacteriorhodopsin.Abbreviations 20 specific gravity at 20°C - Tris Tris-(hydroxymethyl)-aminomethane     

Dopamine release induced by electrical field stimulation of rat hypothalamus invitro: Inhibition by melatonin

Microdissected slices of rat hypothalamus were incubated with ³H -dopamine and then subjected to two successive sets of electrical field stimulation in a superfusion chamber. Neurotransmitter release was found to be calcium dependent and the amount of release was determined by scintillation counting of the effluent buffer. The release obtained following the first train of stimuli served as an internal reference. The samples were exposed to drugs during the interval between the two sets of stimuli. Using this technique, as well as K⁺-evoked depolarization, we were able to show that subnanomolar concentrations of melatonin, the hormone secreted from the pineal gland, inhibits dopamine release from hypothalamic slices. The possibility that melatonin modulates neurotransmission in the brain is therefore indicated.     

An ordered arrangement of chromosomes in the somatic nucleus of common wheat Triticum aestivum L.

Spatial relationships between chromosomes of the same genome, both homologous and non-homologous, were studied in root-tip cells of common wheat, Triticum aestivum (2n = 6x = 42). Mean distance between members of all the 21 homologous pairs (seven in each of the three genomes) and of 45 out of the 63 possible non-homologous combinations of two (21 in each genome) were determined. To minimize disruption of nuclear chromosomal arrangement, the cells were pretreated with cold temperature either in tap water or in a physiological medium (White solution) and distances between cytologically marked chromosomes were measured at metaphase. Comparison of distances for homologues with those for non-homologues indicated clearly that, within each genome, the homologous chromosomes were significantly closer to one another than were the non-homologues. Distances between homologues were similar in all three genomes, as were distances between non-homologues. The data are consistent with the hypothesis that the chromosomes of each genome of common wheat are arranged in the somatic nucleus in a highly specific ordered pattern. In this hypothetical arrangement, homologous chromosomes are closely associated, while the nonhomologues occupy definite positions with respect to one another. The universality of the phenomenon and its cellular mechanism and biological significance are discussed.     

Solubilization of muscarinic acetylcholine receptor by zwitterionic detergent from rat brain cortex

The muscarinic acetylcholine receptor was solubilized from rat brain cortex by zwitterionic detergent 3-[(3-chloramidopropyl) dimethylammonio]-1-propanesulfonate (CHAPS). About 15% of the binding activity was solubilized and 40% of the activity was destroyed by the detergent. Binding of the muscarinic antagonist [³H]-N-methyl-4-piperidyl benzilate (4NMPB) was saturable. Scatchard analysis revealed a single population of binding sites with K_D value of 0.7 nM and a B_max value of 340 fmoles/mg protein. The homogenate and the CHAPS treated pellet and soluble receptors showed similar affinity for the agonists oxotremorine and carbamylcholine and for the antagonists QNB and atropine. The dissociation of 4NMPB from the soluble receptors appears slightly slower than from the membrane bound receptors.     

Versatile Method for Evaluating a Cell Culture by Various Morphological Techniques

Cellulose acetate is a versatile material for evaluating cells grown under identical conditions by various morphological techniques. This inexpensive material is transparent, easily cut to size and shape, nontoxic to cell cultures, and resistant to most chemicals used in histochemistry and in scanning and transmission electron microscopy. Samples may be obtained during and after the culture process. Cellulose acetate slides can be mounted directly over glass slides for direct observation and are easily peeled off plastic blocks for electron microscopy, leaving the cells behind. Relative disadvantages include its autofluorescence and a tendency to soften in strong acids or pure solutions of organic solvents such as xylene and propylene oxide.     

The use of inorganic substances to stimulate gut evacuation in Daphnia magna

Observations were done on the effect of inorganic substances on the gut evacuation process in Daphnia magna. Procedures which accelerate this process are described.