Electronic structure and molecular design of simplified polyimide systems

The electronic structures of newly designed polyimide systems (ethenetetracarboxylic 1,2:1,2-dianhydride-diaminoethyne (PI-A) and ethenetetracarboxylic 1,1:2,2-dianhydride-diaminoethyne(PI-B)) are studied in detail with respect to their optimized geometries on the basis of the one-dimensional tight-binding self-consistent field crystal-orbital method. The computational results have revealed that PI-B shows intriguing properties such as a very small band gap and a wide bandwidth near the frontier level, compared with PI-A and other polyimides. Since PI-B would be a promising candidate for a new electric conducting material, a reaction diagram for this polymer is also proposed.Also affiliated to Central Research Laboratories, Matsushita Electric Industrial Co., Moriguchi 570, Japan.     

Morphology,physics, chemistry and biology of Lake Rara in West Nepal

A survey of oligotrophic Lake Rara, the biggest lake in Nepal, was carried out from 1982 till 1984. Mean depth is 100 m, and maximum depth is 167 m. The surface area covers 9.8 km², and the lake contains 0.98 km³ volume of water. Transparency was about 16 m, photoquantum yield decreased exponentially with depth below 5 m, and the extinction coefficient was 8.3 × 10⁻². The concentration of Chl.-a was in the range of 0.06–0.46 mg m⁻³, and total nitrogen was 18–30 μg 1⁻¹. The whole water column was well oxygenated. Primary productivity was extremely low. It has more than 30 inflowing brooks and one outlet. The water quality of the brooks changes drastically with their location. The pH, electrical conductivity, and EDTA hardness in the waters from a landslide area were high. In the waters from a rich pine forest they were extremely low. The zooplankton consisted of two species of protozoa, five species of rotifers, two species of Cladocera, and two species of Copepoda. The zooplankton density range was 6200–16200 individuals m⁻³. The minimum was on November 11th, 1983 and the maximum on August 19th, 1983.     

Substance K: a novel mammalian tachykinin that differs from substance P in its pharmacological profile

The primary structure of one of the bovine brain substance P precursors has shown the existence of a second mammalian tachykinin sequence, named substance K, that is remarkably homologous to that of the amphibian peptide kassinin. In this study, three substance K sequences were chemically synthesized and were submitted to parallel bioassays with kassinin, substance P and physalaemin. The results show that the three substance K peptides all possess biological activities characteristic of the tachykinin family and that their biological activities more closely resemble those of kassinin than those of substance P or physalaemin. This suggests that substance K may have a physiological role which is related to but different from that of substance P in mammalian organisms.     

Rapid Development of Mitochondria in Pea Cotyledons during the Early Stage of Germination

Rapid increases in activities and components of mitochondrial particles isolated from cotyledons of Pisum sativum var. Alaska during the early stage of germination are described. Respiratory rate of the cotyledons increased rapidly as hydration proceeded. A similar but slightly delayed increase in respiratory activity of the isolated mitochondrial fraction was observed. The respiratory control ratio and adenosine 5′-pyrophosphate/oxygen ratio rose during imbibition. Cytochrome oxidase and malate dehydrogenase activities in the mitochondrial fraction increased during the initial phase of imbibition. The increase seemed to precede that in respiratory activity. A significant activity of cytochrome oxidase and most of the malate dehydrogenase activity in the cotyledons were present in the postmitochondrial fraction in the case of the dry seeds. Mitochondrial protein and phospholipid also increased during imbibition, and the rise in the components seemed to concur with that in respiratory activity. The mechanism of mitochondrial development during imbibition is discussed.     

Nonselective Incorporation into Sporangium of Either “Older” or “Younger” Chromosome of the Vegetative Cell During Sporulation in Bacillus cereus

Employing Bacillus cereus strain 2, we examined the fate of two chromosomes contained in vegetative cells in the course of sporulation. Cytological observations and quantitative estimation of deoxyribonucleic acid (DNA) confirmed the earlier observations that, during the course of sporulation, one of two chromosomes of the vegetative cell was incorporated into the sporangium and the other disappeared into the medium as the result of cell lysis. Log-phase cells, labeled completely with thymine-2-(14)C in the presence of deoxyadenosine, were cultured in the "cold" glucose-glutamate-glycine-salts medium, and culture samples, taken at intervals at successive generations, were subjected to sporulation in glutamate-salts medium. The percentage of radioactivity in the spores separated from each culture remained almost unchanged at nearly 50% and was independent of the number of generations of the preceding culture in the "cold" medium. This suggests that the selective incorporation into the sporangium of either the "older" or "younger" chromosome of a vegetative cell does not occur in the course of spore formation. Some examples of the selective and nonselective behavior of DNA molecules in cellular events in microorganisms are cited.     

Incorporation of tritiated thymidine into mitochondrial DNA of the liver and kidney cells of chickens and mice in tissue culture

Summary ³H-thymidine incorporation into mitochondrial DNA of the liver and the kidney cells of chick embryos and newborn mice in tissue culture was shown by means of electron microscope radioautography with accurate localization. In these cells, about 20% of all the mitochondria were labeled at their matrices between the cristae within 4 hours in contact with the radioisotope, which were removed by DN'ase.From the results, it is clear that the mitochondria of avian and mammalian cells in tissue culture synthesize DNA.     

RecA, Tus protein and constitutive stable DNA replication inEscherichia coli rnhA mutants

Constitutive stable DNA replication (cSDR), which uniquely occurs inEscherichia coli rnhA mutants deficient in ribonuclease HI activity, requires RecA function. TherecA428 mutation, which inactivates the recombinase activity but imparts a constitutive coprotease activity, blocks cSDR inrnhA mutants. The result indicates that the recombinase activity of RecA, which promotes homologous pairing and strand exchange, is essential for cSDR. Despite the requirement for RecA recombinase activity, mutations inrecB, recD, recJ, ruvA andruvC neither inhibit nor stimulate cSDR. It was proposed that the property of RecA essential for homologous pairing and strand exchange is uniquely required for initiation of cSDR inrnhA mutants without involving the homologous recombination process. The possibility that RecA protein is necessary to counteract the action of Tus protein, a contra-helicase which stalls replication forks in theter region of the chromosome, was ruled out because introduction of thetus : :kan mutation, which inactivates Tus protein, did not alleviate the RecA requirement for cSDR.     

Protease resistant interleukin-3 stimulating components in excretory and secretory products from adult worms of Strongyloides ratti.

Excretory and secretory (ES) products collected from adult worms of Strongyloides ratti stimulated interleukin-3 (IL-3) production with mesenteric lymph node cells from infected C57BL/6 mice, but not with normal mesenteric lymph node cells. The IL-3 stimulating components were not major IgG binding antigens. Activity of the IL-3 stimulating components was stable by treatment with protease, although reduced by heating in boiling water.     

Electronic structures of donor-acceptor polymers based on polythiophene,polyfuran and polypyrrole

Theoretical results on the geometric and electronic structures of some donor-acceptor polymers based on polythiophene (X=S), polyfuran (X=O) and polypyrrole (X=NH) were obtained, using a one-dimensional tight-binding self-consistent field crystal-orbital (SCF-CO) method at the MNDO-AM1 level of approximation. The repeat unit of these polymers consits of a bithiophene, furan or bipyrrole unit bridged by an electron-accepting group or. The optimized geometries of the polymers show a strong dependence on the nature of the electron donating group X. All the polymers studied are predicted to have band gap values ranging between 1 eV and 2 eV. An analysis of their -bond order data and of the patterns of their frontier orbitals shows they have benzenoid-like electronic structures.