Binding of heparin to human high molecular weight kininogen

The binding of heparin to high molecular weight kininogen (H-kininogen) was analyzed by the effect of kininogen in decreasing the heparin-induced enhancement of the rate of inactivation of thrombin by antithrombin. The conditions were arranged so that the heparin-catalyzed antithrombin-thrombin reaction, monitored in the presence of the reversible thrombin inhibitor p-aminobenzamidine, followed pseudo-first-order kinetics and the observed rate constant (kappa obsd) varied linearly with the heparin concentration. In the absence of metal ions, H-kininogen minimally affected kappa obsd, measured at a constant concentration of heparin with high affinity for antithrombin (30 nM), at I = 0.15, pH 7.4 and 25 degrees C. However, at a saturating concentration of Zn2+ (10 microM), kappa obsd was reduced to 50% at approximately 20 nM H-kininogen and to that of the uncatalyzed reaction at greater than or equal to approximately 0.2 microM H-kininogen. Conversely, at a saturating concentration of H-kininogen (0.5 microM), kappa obsd was decreased to 50% at approximately 0.6 microM Zn2+ and to the kappa obsd of the uncatalyzed reaction at greater than or equal to 10 microM Zn2+. Other metal ions were effective in the order Zn2+ approximately Ni2+ greater than Cu2+ approximately Co2+ approximately Cd2+. The single-chain and two-chain forms of H-kininogen and the H-kininogen light chain reduced the heparin enhancement in the presence of Zn2+ to the same extent, whereas low molecular weight kininogen had no influence.(ABSTRACT TRUNCATED AT 250 WORDS)     

Melting behavior of a covalently closed, single-stranded, circular DNA

We synthesized the 26-residue deoxynucleotide sequence d(TTCCT5GGAATTCCT5GGAA) which folds intramolecularly to form a dumbbell-shaped, double-hairpin structure with a gap between the 3' and the 5' ends. We used T4 polynucleotide kinase to phosphorylate the 5' end followed by T4 DNA ligase to close the 3' and 5' ends. Melting of the dumbbell structure formed by this ligated sequence produces a covalently closed, single-stranded, circular final state. We employed calorimetric and spectroscopic techniques to characterize thermodynamically the melting behavior of the ligated molecule and compared it with the corresponding melting behavior of its unligated precursor. This comparison allowed us to characterize uniquely the influence of single-stranded ring closure on intramolecular duplex melting. The data reveal that ring closure produces a thermally more stable structure which exhibits significantly altered melting thermodynamics. We rationalize these thermodynamic differences in terms of differential solvation and differential counterion association between the ligated and unligated molecules. We also note the importance of such constrained dumbbell structures as models for hairpins, cruciforms, and locally melted domains within naturally occurring DNA polymers.     

The use of metronidazole, tinidazole and dimetridazole in eliminating trichomonads from laboratory mice

Metronidazole, tinidazole and dimetridazole were administered in the drinking water for 5 days to mice experimentally infected with Tritrichomonas muris and Tetratrichomonas microta. Mice were successfully infected with T. muris and T. microta recovered from infected gerbils. The trichomonas infection was successfully eliminated in mice given a 1% sucrose solution containing 2.5 mg/ml metronidazole or tinidazole. Mice receiving 1.0 mg/ml metronidazole, 1.0 mg/ml tinidazole and 1.2, 5.0 and 10.0 mg/ml dimetridazole failed to eliminate the trichomonas organism. A reduction in water intake was only noted with mice receiving 10 mg/ml dimetridazole. In mice receiving only 1% sucrose the infection was not eliminated.     

Spatial arrangement of tiller replacement in Agropyron desertorum following grazing

Summary The spatial arrangement of tiller replacement was assessed on grazed and ungrazed tussocks of Agropyron desertorum (Fisch. ex Link) Schult. for three annual cycles. Frequency distributions of the number of replacement tillers per single progenitor were also determined. Tiller replacement was usually greater on the perimeter of tussocks than within the core, with or without grazing. Replacement was inversely related to grazing intensity, both on the perimeter and within the core of tussocks. Heights of replacement tillers on the perimeter or within the core seldom differed. Furthermore, grazing seldom affected the number of replacement tillers per progenitor. Greater tillering on the perimeter than within the core indicates that the tussocks were expanding. Apparently, grazing neither enhances tussock expansion and subsequent disintegration, nor does it necessarily lead to patches of tillers (multiple tillering per progenitor) within tussocks of A. desertorum.     

cDNA and deduced primary structure of rat protein B23, a nucleolar protein containing highly conserved sequences

Protein B23 (Mr/pI = 38,000/5.1) is a major RNA-associated nucleolar phosphoprotein which contains highly acidic segments and has a high affinity for silver ions. Using synthetic oligonucleotides as probes cloned cDNAs encoding protein B23 were isolated and characterized. One of the cDNAs, obtained from a rat brain library, contained an insert of 1232 base pairs of DNA encoding a polypeptide of 292 amino acid residues. Segments of the protein sequence were confirmed by partial sequencing of CNBr fragments from rat hepatoma protein B23. The protein contains a methionine-rich amino-terminal sequence and two highly acidic segments in the center of the sequence. The first acidic segment, in which 11 of the 13 residues are acidic, begins at residue 120 and contains a major phosphorylation site. In the second segment (residues 159-187) there are four copies of the sequence Asp-Asp-Glu, and all but two of the 29 residues have acidic side chains. When the sequence of the rat protein was compared with available sequences from other species a high degree of conservation was found; the 77-residue carboxyl-terminal sequence is identical with that of human protein B23 (Chan, P. K., Chan, W.-Y., Yung, B. Y. M., Cook, R. G., Aldrich, M. B., Ku, D., Goldknopf, I. L., and Busch, H. (1986) J. Biol. Chem. 261, 14335-24341), and about 63% of the residues are identical when the rat B23 sequence is compared with protein N038 from Xenopus laevis (Schmidt-Zachmann, M. S., Hügle-D?rr, B., and Franke, W. (1987) EMBO J. 6, 1881-1890). Except for the presence of highly acidic regions no significant similarities were found with protein C23 (nucleolin), the other major nucleolar protein.     

Characterization of cross-bridge elasticity and kinetics of cross-bridge cycling during force development in single smooth muscle cells

Force development in smooth muscle, as in skeletal muscle, is believed to reflect recruitment of force-generating myosin cross-bridges. However, little is known about the events underlying cross-bridge recruitment as the muscle cell approaches peak isometric force and then enters a period of tension maintenance. In the present studies on single smooth muscle cells isolated from the toad (Bufo marinus) stomach muscularis, active muscle stiffness, calculated from the force response to small sinusoidal length changes (0.5% cell length, 250 Hz), was utilized to estimate the relative number of attached cross-bridges. By comparing stiffness during initial force development to stiffness during force redevelopment immediately after a quick release imposed at peak force, we propose that the instantaneous active stiffness of the cell reflects both a linearly elastic cross-bridge element having 1.5 times the compliance of the cross-bridge in frog skeletal muscle and a series elastic component having an exponential length-force relationship. At the onset of force development, the ratio of stiffness to force was 2.5 times greater than at peak isometric force. These data suggest that, upon activation, cross-bridges attach in at least two states (i.e., low-force-producing and high-force-producing) and redistribute to a steady state distribution at peak isometric force. The possibility that the cross-bridge cycling rate was modulated with time was also investigated by analyzing the time course of tension recovery to small, rapid step length changes (0.5% cell length in 2.5 ms) imposed during initial force development, at peak force, and after 15 s of tension maintenance. The rate of tension recovery slowed continuously throughout force development following activation and slowed further as force was maintained. Our results suggest that the kinetics of force production in smooth muscle may involve a redistribution of cross-bridge populations between two attached states and that the average cycling rate of these cross-bridges becomes slower with time during contraction.     

Dexamethasone blocks increased leukotriene B4 production during endotoxin-induced lung injury

We hypothesized that leukotriene B4 (LTB4) might be produced during endotoxemia in pigs and, if so, might play a role in the pathophysiology of acute respiratory failure. Escherichia coli endotoxin (055-B5) was infused intravenously into anesthetized pigs at 5 micrograms/kg the 1st h, followed by 2 micrograms.kg-1.h-1 for 3 h. Endotoxemic pigs were treated with dexamethasone (DEX, iv) 18 h (5 mg/kg) and 1 h (5 mg/kg) before onset of endotoxemia. During phases I (i.e., 0-2 h) and II (i.e., 2-4 h), endotoxin decreased cardiac index, caused granulocytopenia, and increased mean pulmonary arterial pressure, pulmonary vascular resistance, alveolar-arterial O2 gradient, and hematocrit. During phase II, plasma LTB4 levels were increased (as determined by radioimmunoassay, reverse-phase high-performance liquid chromatography, and ultraviolet spectroscopy). Endotoxin increased the levels of LTB4 and albumin in bronchoalveolar lavage fluid (BALF). DEX blocked or greatly attenuated the endotoxin-induced hemodynamic abnormalities and blocked the increases in plasma and BALF LTB4 levels. We conclude that LTB4 is produced during porcine endotoxemia and could possibly play a role in the pathophysiology of endotoxin-induced lung injury in anesthetized pigs.     

Viability Tests for Thick Walled Fungal Spores (ex: Oospores of Peronospora manshurica)

Oospores of Peronospora manshurica, the causal agent of soybean downy mildew, were stained by a variety of techniques. TTC (tetrazolium chloride) and NBT (nitroblue tetrazolium chloride) primarily stained oospores which were cytologically abnormal and appeared degenerating. Cytological normal oospores were not stained by these compounds presumably because the dyes were excluded from the oospore cytoplasm by the oospore wall or the plasmalemma. Strong autofluorescence of dead/degenerating oospores in the FDA test (fluorescein diacetate) made scoring of the oospore viability by this technique unreliable. Phloxine B was found in a consistent way to stain the degenerating oospores and a small proportion of the oospores which by light microscopic, observations could not be scored cytologically abnormal. Control experiments with live and dead cells of yeast (Saccharomyces cerevisiae) confirm that phloxine B is excluded from live cells and dead cells become stained. The presumed mode of action is that the semipermeability of the plasma membrane of live cells excludes the stain. The phloxine B test described here appears a promising technique for the determination of oospore viability of P. manshurica.     

Characterization of the postacrosomal sheath of bovine spermatozoa

A purified head fraction was prepared from bovine epididymal spermatozoa and was utilized to identify the solubility characteristics and major polypeptide components of the postacrosomal sheath. Sperm heads extracted in nonionic-detergent-containing or high-salt-containing solutions retained an intact postacrosomal sheath, but it was readily solubilized by high pH extraction solutions. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a major polypeptide of 58,000 daltons (58-kD) in the high pH extract solution. Antibodies to the 58-kD polypeptide specifically reacted with the postacrosomal segment by immunofluorescence and by electron microscopic immunohistochemistry were shown to bind the postacrosomal sheath. We conclude that this 58-kD polypeptide is a constituent of the postacrosomal sheath and that its distribution is restricted to the postacrosomal segment.