A modulating role of mercurials-sensitive sulfhydryl groups in synaptic GABA receptor binding

The specific binding of GABA (γ-aminobutyric acid) agonist ³H-muscimol, to synaptic membranes from the rat brain showed a significant increase, when the membranous preparations were treated with a low concentration (10^?4–10^?5M) of mercurial sulfhydryl reagents such as p-chloromercuribenzoate and mercuric chloride. This activation in GABA receptor binding was bicuculline-sensitive, and was partially restored by subsequent treatments with 10 mM cysteine, penicillamine, or mercaptoethanol. Scatchard analysis of the binding revealed that this activation was due to the increase in the affinity of both high and low affinity bindings sites but not in the B_max values. On the other hand, the treatment of synaptic membranes with hydrophilic sulfhydryl reagents such as N-ethylmaleimide and iodoacetate had no effect on the binding. These hydrophilic sulfhydryl reagents, however, induced an increase of the binding following the pretreatment of synaptic membranes with 0.01% Triton X-100 or 0.5 U/mg prot. of phospholipase A₂ (EC 3.1.1.4.). These results suggest that mercurials-sensitive sulfhydryl groups, which are normally masked by membrane lipids, may play a modulating role in GABA receptor binding at central synapses.     

IS50-mediated inverse transposition. Discrimination between the two ends of an IS element

The crystal and molecular structure of l-pyroglutamyl-β-(2-thienyl)-l-alanyl-l-prolinamide, < Glu-Thi-Pro-NH₂(Thi²-TRH), C₁₇H₂₂N₄O₄S, has been determined from X-ray diffraction data. Thi²-TRH is a highly active analogue of thyroliberin, a thyrotropin-releasing hormone (TRH), in which the imidazole ring of the central histidine moiety in the natural hormone has been replaced by a 2-thienyl group. Thi²-TRH crystallizes from water in the monoclinic space group P2₁, $\text{a = 9.340(1)}\text{A}\text{?}\text{, b = 21.961(3)}\text{A}\text{?}\text{, c = 9.449(1)}\text{A}\text{?}$ and β = 109.58(1) °, with two molecules per asymmetric unit. These independent molecules, A and B, have the same general backbone conformation with the φ₂, ψ₂ and ψ₃ torsional angles close to ?90 °, +120 ° and +150 °, respectively, but they show different magnitudes of rotational disorder in the thiophene ring as well as a certain disorder in the pyrrolidine ring. A and B are cross-linked by four interchain hydrogen bonds, forming a two-stranded antiparallel β-pleated sheet structure. The molecules in these dimer fragments are further hydrogen-bonded to successive translated molecules along the a and c axes, forming a pronounced two-dimensional predominantly hydrophobic layer structure. These layers, in which the atoms are almost equally arranged on both sides, are separated by ordinary van der Waals' distances. A close correlation between the molecular conformation in the solid state and the preferential conformation in solution is found. It is concluded that the crystalline structure of Thi²-TRH possesses structural features which may be of relevance in the hormone-receptor interaction process.     

Isolation and characterization of plasmid-deletion derivatives from an Hfr made with Rts1 plasmid carrying a chromosomal mutation, plt

Summary Rts1 is a kanamycin-resistance plasmid and multiphenotypically thermosensitive. The detrimental host cell growth at 42° C is expressed only when it exitst autonomously but not in an integrated state. However, a cholate-resistant (plt) mutant of the Hfr with an integrated Rts1 plasmid was found to be thermosensitive like a strain with the same plasmid autonomoulsy. This thermosensitivity depends on the existence of the integrated plasmid. Deletion derivatives of integrated plasmid genome from this Hfr strain were isolated with or without thermal selective growth at 42° C and mapping of the plasmid was attempted by analyzing them. A total of 141 kanamycin-sensitive derivatives were independently isolated and examined for their thermosensitivity (genetic locus: tsg), incompatibility (genetic locus: incT), conjugal fertility (genetic locus: tra), restriction of T4 phase (two genetic loci: resA and resB) and for DNase activity (genetic locus: dns). On the basis of characterization of 141 deletion derivatives, they were divided into 15 patterns which would correspond to a linear map integrated into the chromosome: ... resA ... dns ... resB ... tra ... kan ... incT ... tsg ... It is noteworthy that restriction of T4D phage is determined by two distinct genes, resA and resB, intervened by dns and that propagation of T4D phage on a strain with a resA ⁺ resB ^- genome failed to produce modified progeny phages.     

Physiological polyspermy: Selection of a sperm nucleus for the development of diploid genomes in amphibians

The union between a sperm and an egg nucleus in egg fertilization is necessary to mix genetic materials to create a new diploid genome for the next generation. In most animals, only one sperm is incorporated into the egg (monospermy), but several animals exhibit physiological polyspermy in which several sperms enter the egg during normal fertilization. However, only one sperm nucleus forms the zygote nucleus with the egg nucleus, even in a polyspermic egg. The cellular and molecular mechanisms involved in the selection of sperm nuclei in the egg cytoplasm have been well investigated in urodele amphibians. The principal sperm nucleus develops a larger sperm aster and contacts the egg nucleus to form a zygote nucleus, whereas other accessory sperm nuclei are unable to approach the egg nucleus. The diploid zygote nucleus induces cleavage and participates in embryonic development, whereas the accessory sperm nuclei undergo pyknosis and degenerate. We propose several models to account for the mechanisms of the selection of one sperm nucleus and the degeneration of accessory sperm nuclei. The roles of physiological polyspermy in animal reproduction are discussed by comparison with other polyspermic species.     

Factors determining vegetation recovery after abandonment of coal-mining villages

Landscape and Ecological Engineering - There have been many earlier studies of the biodiversity and ecosystem services of abandoned farmlands, but studies of abandoned villages are limited,...     

Export of dissolved iron from river catchments in northeast Japan

Landscape and Ecological Engineering - This study investigated the export of dissolved iron (DFe) from river catchments with emphasis on land use and land cover (LULC). The DFe concentrations were...     

Ribosylation of the Base Residue of Inosine Derivatives by Phase-Transfer Catalysis

Abstract

Reaction of 2′,3′,5′-O-silylated inosine derivative 1 with 2, 3-O-isopropylidene-5-O-tritylribosyl chloride (3) in a two-phase (CH₂Cl₂-aq. NaOH) system in the presence of Bu₄NBr gave three products, i. e., 6-O-α-, 6-O-β-, and N ¹-β-isomers of glycosides 4, 5a, and 5b. A similar PTC reaction of 1 with 2, 3, 5-tri-O-benzylribosyl bromide (9) gave four regio- and stereo-isomers involving the N¹-β-glycoside 10. Reaction of 1 with 2, 3, 5-tri-O-benzoylribosyl bromide (11) afforded three products involving the desired N¹-β-glycoside 12b, which could be deprotected to give N ¹-ribosylinosine (15b) as a useful intermediate for the synthesis of cIDPR.

     

Ophiocordyceps sessilis sp. nov., a new species of Ophiocordyceps on Camponotus ants in Japan

Ophiocordyceps sessilis, a new species of Ophiocordycipitaceae, Hypocreales, was found on Camponotus obscuripes ants, where the ants were primarily infected by another close relative, O. pulvinata. Morphological observation clearly indicated that O. sessilis and O. pulvinata are distinct species. Ophiocordyceps sessilis exhibited superficial development of perithecia and ascospore disarticulation into part-spores, not known in O. pulvinata. Nucleotide sequence data suggested that O. sessilis belongs in Ophiocordyceps, Ophiocordycipitaceae. Molecular data also indicated that O. sessilis is a close relative of O. cuboidea, O. prolifica, O. paracuboidea, and O. ryogamiensis, which are all known to produce part-spores. Since O. sessilis is always associated with ants infected by O. pulvinata, O. sessilis may be a hyperparasite of O. pulvinata.