Structural and sequence diversity of the pathogenicity island of uropathogenic Escherichia coli which encodes the USP protein

A total of 321 uropathogenic Escherichia coli (UPEC) strains and 12 strains of E. coli isolated from stool samples of healthy individuals, which were previously shown to be positive in colony hybridization test using the usp (encoding for the uropathogenic-specific protein) DNA probe, were examined by PCR amplification to determine the size of the usp gene and the pathogenicity island (PI). Three types of size variation were observed for the usp gene and four types for the PI. Sequencing analysis of the PIs from seven representative strains (six UPEC and one from a normal healthy individual) revealed that the usp genes can be classified into two groups, each having different sequences in the 3'-terminal region. The peptides encoded by the three open reading frames (ORFs) downstream of usp had identical 23 amino acid residues in the C-terminal region. The subregion encoding these small ORFs has a mosaic structure constituted of six segments. The positions of these segments vary from strain to strain, and in some strains, two to four segments are deleted. This indicates that rearrangements occur frequently in this region and the mosaic arrangement apparently contributes to the size variation observed in the PCR examination of the usp genes and PIs.     

Different sensitivities to agonist of muscarinic acetylcholine receptor subtypes

Muscarinic acetylcholine receptor (mAChR) III expressed in Xenopus oocytes, like mAChR I, mediates activation of a Ca²⁺-dependent Cl⁻ current, whereas mAChR IV, like mAChR II, principally induces activation of Na⁺ and K⁺ currents in a Ca²⁺-independent manner. mAChR III has a sensitivity to agonist of about one order of magnitude higher than that of mAChR I in mediating the Ca²⁺-dependent current response in Xenopus oocytes and in stimulating phosphoinositide hydrolysis in NG108-15 neuroblastoma-glioma hybrid cells. The agonist-binding affinity of mAChR III is also about one order of magnitude higher than that of mAChR I.     

Peroxidase-catalyzed benzidine binding to DNA and other macromolecules

[14C]Benzidine is rapidly oxidized by a peroxidase/H2O2 system to products which bind irreversibly to DNA. The presence of exogenous DNA also prevented benzidine polymerization to 'benzidine brown' and azobenzidine. Two molar equivalents of H2O2 were required to oxidize the benzidine and achieve maximal DNA binding. Furthermore, 95% of the benzidine was trapped and 36 nmol benzidine was bound per mg DNA. Polyriboguanylic acid was as effective as DNA in binding benzidine, but polyriboadenylic acid, polyribouridylic acid and polyribocytidylic acid were much less effective. Binding of [14C]benzidine correlated well with the absorbance at 295 nm and 390 nm of the modified DNA or various synthetic homopolymers of ribonucleotides isolated from the reaction mixture. The peroxidase/H2O2 system also catalyzed the binding of dichlorobenzidine, o-tolidine and o-dianisidine to DNA but 3,5,3',5'-tetramethylbenzidine, a non-carcinogen, did not bind. The binding could be prevented by various biological hydrogen donors, thiols, or phenolic antioxidants. The mechanisms for DNA protection were investigated; the oxidized benzidine species involved in binding can be reduced with ascorbate, NADPH, or thiols, and trapped by thiols or phenolic antioxidants to form conjugates or adducts.     

Difference equation model of the entrainment of myocardial pacemaker cells based on the phase response curve

As a method for investigating entrainment phenomena found in biological oscillations, a model is presented which is formulated as a set of difference equations on the basis of phase response curves of biological oscillators. Properties of the model are discussed and synchronization of cardiac pacemaker cells to the external periodic stimuli is analyzed by use of the model. It is shown that the model is reducible to an equivalent system to the mathematical neuron model of Nagumo et al. under a specific parametric condition of the phase response curve. As an application to the cardiac arrhythmias, the model of ventricular parasystoles studied by Moe et al. is described mathematically in terms of a system of difference equations. In addition, a more comprehensive model of ventricular parasystoles is proposed.     

Zinc Inhibition of t-[3H]Butylbicycloorthobenzoate Binding to the GABAA Receptor Complex

Abstract: The effect of Zn²⁺ on t -[³H]butylbicycloorthobenzoate ([³H]TBOB) binding to the GABA_A receptor complex was studied autoradiographically in rat brain. Zn²⁺ inhibited [³H]TBOB binding in a dose-dependent manner at physiological concentrations. Saturation analysis revealed noncompetitive inhibition in various brain regions. The inhibitory effect of Zn²⁺ had regional heterogeneity; regions showing the greatest inhibition of [³H]TBOB binding were cortical laminae I–III, most areas of hippocampus, striatum, septum, and cerebellar cortex. Regions with relatively less inhibition of [³H]TBOB binding included cortical laminae V–VI, thalamus, superior colliculus, inferior colliculus, and central gray matter. The effect of Zn²⁺ and those of other GABA_A ligands, such as benzodiazepines, bicuculline, isoguvacine, and picrotoxin, on [³H]TBOB binding seemed to be additive. Ni²⁺, Cd²⁺, and Cu²⁺ also inhibited [³H]TBOB binding with a regional heterogeneity similar to that produced by Zn²⁺. These results are consistent with Zn²⁺ acting at the previously detected recognition site on the GABA_A receptor complex, distinct from the picrotoxin, GABA, and benzodiazepine sites. The regional heterogeneity of the Zn²⁺ effect may reflect differential regional distribution of GABA_A receptor subtypes among brain regions. Other divalent cations probably act at the Zn²⁺ binding site.     

Identification and biological activity of novel peptidomimetic gastrin/CCK-B receptor agonists

The design, synthesis and biological activity of two novel series of compounds derived from the basic Boc-CCK-4 structure which provide potent ligands for the gastrin/CCK-B receptor is outlined. Within these series, new pseudopeptide compounds were discovered which unexpectedly were functional agonists in vivo, as shown by their ability to stimulate basal gastric acid secretion in rats, an effect which was blocked by the potent gastrin/CCK-B receptor antagonist YM022.     

A facile synthesis of 5-thio- -fucose and 5-thio- -arabinose from -arabinose

5-Thio- -fucopyranose tetraacetate was synthesized in 11 steps from or -arabinose diethyl dithioacetal by one-carbon elongation at C-5. Highly diastereo-selective addition of MeLi in ether to a

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derivative was achieved to give the corresponding 6-deoxy-β- -altrofuranose isomer in good yield. A sulfur atom was introduced at C-5 of 6-deoxy- -altrofuranose derivatives via substitution of a 5-tosylate with KSAc in HMPA with inversion of configuration, giving 5-thio- -fucopyranose. A derivative was also prepared from 6-deoxy-β- -altrofuranose derivatives. 5-Thio- -arabinopyranose tetraacetate, the 5-demethyl analog of 5-thio- -fucose, was also synthesized from in 5 steps. 5-Thio- -arabinose showed weak inhibitory activity against α- -fucosidase from bovine kidney (K_{i = 0.77 mM}).     

Dissociation of Limulus polyphemus (horseshoe crab) hemocyanin. I. Solution X-ray scattering study in equilibrium

A solution X-ray scattering study has been performed on Limulus polyphemus (horseshoe crab) hemocyanin and its dissociated fragments at various pH values in the presence and absence of Ca2+. The scattering patterns of native hemocyanin (48-mer), the half molecule (24-mer), quarter molecule (12-mer) and monomer fraction were measured. The radii of gyration for the four molecular species were calculated from the Guinier plots to be 110.7, 91.3, 77.3, and 36.5 A, respectively. Models which yield good fits to the experimental data are presented. The models were constructed using eight, four and two spheres with a radius of 58 A, assuming the sphere to be the submultiple composed of six subunits. The radii of gyration were calculated on the basis of the model and the values found to be 106, 94 and 73 A, respectively, in good agreement with the experimental results.     

The effect of adenosine on the fluorescence responses of chlorotetracycline-loaded human polymorphonuclear leukocytes

Chlorotetracycline has been used in human polymorphonuclear leukocytes as a probe to investigate the state of membrane-bound calcium. We examined the effect of adenosine on the fluorescence responses of CTC-loaded PMNs stimulated with the synthetic chemotactic peptide, formyl-methionyl-leucyl- phenylalanine. Adenosine inhibited the decrease in CTC fluorescence in a dose-dependent fashion and its effect was reversed by theophylline, an adenosine receptor antagonist. Removal of extracellular adenosine by incubating PMNs with adenosine deaminase abolished the effect of adenosine. These data suggest that adenosine inhibits the release of membrane-bound calcium in PMNs that normally occurs in response to chemotactic stimuli, acting via PMN surface adenosine receptors.