Influence of substituent modifications on the binding of 2-amino-1,8-naphthyridines to cytosine opposite an AP site in DNA duplexes: thermodynamic characterization

Here, we report on a significant effect of substitutions on the binding affinity of a series of 2-amino-1,8-naphthyridines, i.e., 2-amino-1,8-naphthyridine (AND), 2-amino-7-methyl-1,8-naphthyridine (AMND), 2-amino-5,7-dimethyl-1,8-naphthyridine (ADMND) and 2-amino-5,6,7-trimethyl-1,8-naphthyridine (ATMND), all of which can bind to cytosine opposite an AP site in DNA duplexes. Fluorescence titration experiments show that the binding affinity for cytosine is effectively enhanced by the introduction of methyl groups to the naphthyridine ring, and the 1:1 binding constant (10⁶ M⁻¹) follows in the order of AND (0.30) < AMND (2.7) < ADMND (6.1) < ATMND (19) in solutions containing 110 mM Na⁺ (pH 7.0, at 20°C). The thermodynamic parameters obtained by isothermal titration calorimetry experiments indicate that the introduction of methyl groups effectively reduces the loss of binding entropy, which is indeed responsible for the increase in the binding affinity. The heat capacity change (ΔC_p), as determined from temperature dependence of the binding enthalpy, is found to be significantly different between AND (−161 cal/mol K) and ATMND (−217 cal/mol K). The hydrophobic contribution appears to be a key force to explain the observed effect of substitutions on the binding affinity when the observed binding free energy (ΔG_obs) is dissected into its component terms.     

Genetic control of the immune response in lines of chickens selected for graft-versus-host competences

The immune response of chickens to goat erythrocytes has been examined. The H line selected for high competence of graft-versus-host reaction (GVHR) showed higher immune responses than the L line selected for low GVHR competence. It appeared also that immune responses were controlled by the B blood group locus, which is the major histocompatibility locus in chickens. The relative immune responsiveness of B genotypes were B ¹¹/¹¹> B ⁹/ B ¹¹> B ⁹/B⁹.
Treatment of antiserum with 2-mercaptoethanol (2-ME) proved that the difference in immune responses between lines was due mainly to the 2-ME resistant antibody and that the difference between the B genotypes was due to the 2-ME sensitive antibody.     

Lateral conductance parallel to membrane surfaces: effects of anesthetics and electrolytes at pre-transition.

The effects of dilute salts and anesthetics were studied on the impedance dispersion in the dipalmitoylphosphatidylcholine (DPPC) liposomes. Below the pre-transition temperature, the apparent activation energy for conductance in DPPC-H2O without salts was equivalent to pure water, 18.2 kJ mol-1. This suggests that the mobile ions (H3O+ and OH-) interact negligibly with the lipid surface below the pre-transition temperature. At pre-transition temperature, the apparent activation energy of the conductance decreased by the increase in the DPPC concentrations. The effects of various salts (LiCl, NaCl, KCl, KBr, and KI) on the apparent activation energy of the conductance were studied. Changes in anions, but not in cations, affected the activation energy. The order of the effect was Cl- less than Br- less than I-. Cations appear to be highly immobilized by hydrogen bonding to the phosphate moiety of DPPC. The smaller the ionic radius, the more ions are fixed on the surface at the expense of the free-moving species. The apparent activation energy of the transfer of ions at the vesicle surface was estimated from the temperature-dependence of the dielectric constant, and was 61.0 kJ mol-1 in the absence of electrolytes. In the presence of electrolytes, the order of the activation energy was F- greater than Cl- greater than Br- greater than I-. When the ionic radius is smaller, these anions interact with the hydration layer at the vesicle surface and the ionic transfer may become sluggish. In the absence of electrolytes, the apparent activation energy of the dielectric constant decreased by the increase in halothane concentrations. In the presence of electrolytes, however, the addition of halothane increased the apparent activation energy. We propose that the adsorption of halothane on the vesicle surface produces two effects: (1) destruction of the hydration shell, and (2) increase in the binding of electrolytes to the vesicle surface. In the absence of electrolytes, the first effect predominates and the apparent activation energy is decreased. In the presence of electrolytes, the latter effect predominates and the apparent activation energy is increased.     

Inhibition of Bacterial Translocation from the Gastrointestinal Tract of Mice Injected with Cyclophosphamide

Effects of intraperitoneal injection of cyclophosphamide, an immunosuppressant, on the degree of bacterial translocation and morphological changes of Peyer's patches (PP) in the intestine were investigated with antibiotic-decontaminated SPF mice and germfree mice monoassociated with Escherichia coli C25. It has been reported that treatment with cyclophosphamide induces bacterial translocation. Cyclophosphamide treatment in this study, however, significantly decreased E. coli C25 translocation from the gastrointestinal tract to the mesenteric lymph nodes (MLN), although the numbers of lymphoid cells, especially B cells, in the PP, MLN, and spleen were remarkably reduced. Four injections of cyclophosphamide at a dose of 100 mg/kg inhibited bacterial translocation more than one injection at a dose of 200 mg/kg in SPF mice. Germfree mice, however, treated with one dose of 200 mg/kg showed the same inhibition of bacterial translocation as those given 100 mg/kg four times. In cyclophosphamide-treated mice, lymph follicles in the PP were obviously smaller than those in control mice, M-cells were similar in appearance to absorption epithelial cells except for short microvilli, and immune cells among the M-cells had disappeared. These data suggested that inhibition of bacterial translocation in mice treated with cyclophosphamide may be the result of morphological and physiological changes of epithelial cells in the gastrointestinal tract, especially M-cells, as a point of entry of invading bacteria, independent of the changes in immunological function. Received: 16 November 1995 / Accepted: 12 December 1995     

Effect of butyrate on the expression of the human preprourokinase gene introduced into Chinese hamster ovary cells

A plasmid containing the human preprourokinase gene cDNA under the control of the simian virus 40 early region promoter was introduced into CHO-K1 cells and recombinant cell lines secreting a relatively high level of urokinase were obtained. In the course of studying the effects of various agents on the recombinant cell lines, we found that exposure of recombinant cells to 5 mM butyrate for 24 hours resulted in a 2-3 fold increase in urokinase production. The induction by butyrate was dose-dependent. The half maximal dose was approximately 2 mM; maximal stimulation occurred at 5-10 mM. Cell growth, on the other hand, was inhibited by butyrate concentrations greater than 2.5 mM. The response of cells to butyrate was rapid: a significant increase in urokinase production was observed 6 hours after exposure to 5 mM butyrate. Butyrate treatment increased not only the extracellular level but also the intracellular level of urokinase.     

Similarity of rocky intertidal assemblages along the Pacific coast of Japan: effects of spatial scales and geographic distance

Factors and processes affecting community structures operate at various spatial and temporal scales. We analyzed how similarities of rocky intertidal assemblages vary at different spatial scales using a nested, hierarchical sampling design. Intertidal assemblages consisting of algae, sessile animals, and mobile animals were censused on five rock walls at each of five shores chosen within each of six regions along the Pacific coast of Japan, encompassing 1,800 km of coastlines. Based on this sampling design, similarities in assemblages were calculated using both qualitative (presence/absence) and quantitative (percent cover and density) data, and compared at three spatial levels: (1) rock level (the finest spatial scale, encompassing several to hundreds of meters), (2) shore level (the intermediate spatial scale, encompassing several to tens of kilometers), and (3) region level (the broadest spatial scale, encompassing hundreds to thousands of kilometers). Cluster analysis showed that assemblages were categorized into distinct regional groups except for the two southern regions, but they did not separate clearly from each shore. A nested analysis of similarities revealed significant variation in similarities among regions and among shores within each region, with the former showing greater variation. Similarity was negatively correlated with geographic distance at the regional level but not at the shore or the rock levels. At the regional level, similarity decreased more rapidly with distance for mobile animals than sessile organisms. The analyses highlighted the importance of broad-scale abiotic/biotic factors such as oceanic current conditions and biogeographic factors in determining observed patterns in similarity of rocky intertidal assemblages.     

Ecological studies on the timberline of Mt. Fuji

To compare the nutrient economy of woody plants at timberline of Mt. Fuji, seasonal changes in nitrogen content in leaves were examined. There was remarkable difference in seasonal changes in leaf nitrogen content betweenAlnus maximowiczii and other deciduous trees at same habitat.A. maximowiczii scarcely withdrew the leaf nitrogen to woody part during the shedding period, while the other species withdrew about half of the leaf nitrogen to woody part.