IN VITRO ALLELOPATHIC INHIBITION OF NITRIFICATION BY BALSAM POPLAR AND BALSAM FIR

A soil percolation apparatus was used to study the effect of plant extracts on nitrification. Foliar leachates, leaf extracts, and bud extracts of balsam fir (Abies balsamea) and balsam poplar (Populus balsamifera) were added to the ammonium percolation solution. Color tests and quantitative measurement of residual ammonium and formed nitrate were applied. Foliar leachates of balsam fir strongly inhibited nitrification; leachates of balsam poplar were slightly less inhibitory. Balsam fir needle and balsam poplar dormant bud extracts (5% w/v) completely prevented the oxidation of ammonium. The same estracts (2% w/v) still prevented the oxidation of ammonium to nitrate to a large extent. Once again balsam fir extracts inhibited the process more strongly than balsam poplar. No evidence was obtained for the presence of a specific inhibitor of nitrifier microorganisms.     

The crystal structure of PCSK9: a regulator of plasma LDL-cholesterol

Proprotein convertase subtilisin kexin type 9 (PCSK9) has been shown to be involved in the regulation of extracellular levels of the low-density lipoprotien receptor (LDLR). Although PCSK9 is a subtilase, it has not been shown to degrade the LDLR, and its LDLR-lowering mechanism remains uncertain. Here we report the crystal structure of human PCSK9 at 2.3 A resolution. PCSK9 has subtilisin-like pro- and catalytic domains, and the stable interaction between these domains prevents access to PCSK9's catalytic site. The C-terminal domain of PCSK9 has a novel protein fold and may mediate protein-protein interactions. The structure of PCSK9 provides insight into its biochemical characteristics and biological function.     

An analytical model of traumatic diffuse brain injury

Diffuse axonal injury (DAI) with prolonged coma has been produced in the primate using an impulsive, rotational acceleration of the head without impact. This pathophysiological entity has been studied subsequently from a biomechanics perspective using physical models of the skull-brain structure. Subjected to identical loading conditions as the primate, these physical models permit one to measure the deformation within the surrogate brain tissue as a function of the forces applied to the head. An analytical model designed to approximate these experiments has been developed in order to facilitate an analysis of the parameters influencing brain deformation. These three models together are directed toward the development of injury tolerance criteria based upon the shear strain magnitude experienced by the deep white matter of the brain. The analytical model geometry consists of a rigid, right-circular cylindrical shell filled with a Kelvin-Voigt viscoelastic material. Allowing no slip on the boundary, the shell is subjected to a sudden, distributed, axisymmetric, rotational load. A Fourier series representation of the load allows unrestricted load-time histories. The exact solution for the relative angular displacement (V) and the infinitesimal shear strain (epsilon) at any radial location in the viscoelastic material with respect to the shell was determined.(ABSTRACT TRUNCATED AT 250 WORDS)     

FTIR and UV spectroscopy studies of triplex formation between alpha-oligonucleotides with non-ionic phoshoramidate linkages and DNA targets

The triplexes formed by pyrimidine alpha-oligodeoxynucleotides, 15mers alpha dT(15) or 12mers alpha dCT having dimethoxyethyl (PNHdiME), morpholino (PMOR) or propyl (PNHPr) non-ionic phosphoramidate linkages with DNA duplex targets have been investigated by UV and FTIR spectroscopy. Due to the decrease in the electrostatic repulsion between partner strands of identical lengths all modifications result in triplexes more stable than those formed with unmodified phosphodiester beta-oligodeoxynucleotides (beta-ODNs). Among the alpha-ODN third strands having C and T bases and non-ionic phosphoramidate linkages (alpha dCTPN) the most efficient modification is (PNHdiME). The enhanced third strand stability of the alpha dCTPN obtained as diastereoisomeric mixtures is attenuated by the steric hindrance of the PMOR linkages or by the hydrophobicity of the PNHPr linkages. All alpha dCTPN strands form triplexes even at neutral pH. In the most favorable case (PNHdiME), we show by FTIR spectroscopy that the triplex formed at pH 7 is held by Hoogsteen T*A.T triplets and in addition by an hydrogen bond between O6 of G and C of the third strand (Tm = 30 degrees C). The detection of protonated cytosines is correlated at pH 6 with a high stabilization of the triplex (Tm = 65 degrees C). While unfavorable steric effects are overcome with alpha anomers, the limitation of the pH dependence is not completely suppressed. Different triplexes are evidenced for non pH dependent phosphoramidate alpha-thymidilate strands (alpha dT(15)PN) interacting with a target duplex of identical length. At low ionic strength and DNA concentration we observe the binding to beta dA(15) either of alpha dT(15)PN as duplex strand and beta dT(15) as third strand, or of two hydrophobic alpha dT(15)PNHPr strands. An increase in the DNA and counterion concentration stabilizes the anionic target duplex and then the alpha dT(15)PN binds as Hoogsteen third strand.     

Immunohistochemical localization of tonin in rat salivary glands and kidney

Summary As a part of a microfluorometric investigation of the nucleoproteins of nuclei whose chromatin displays varying degrees of condensation, a comparison was made of mouse small thymocyte and hepatocyte nuclei stained with the acidic dye, brilliant sulfaflavine, at pH 2.8. These estimates of total protein content were compared with measurements obtained in similarly stained nuclei after extraction either with 0.4 N H₂SO₄ to remove all histones or with 0.35 M NaCl to remove nucleoplasmic proteins and some loosely bound non-histone chromosomal proteins. Treatment with 5% TCA at 60°C was used to remove nucleic acids and to reverse the effects of formaldehyde fixation. In all instances, the fluorescence of 2c hepatocyte nuclei greatly exceeded that of similarly treated thymocyte nuclei. While extraction with 0.4 N H₂SO₄ resulted in reductions of as much as 75% of the total fluorescence of small thymocyte nuclei, the losses of fluorescence in 2c hepatocyte nuclei amounted to only 20–30%. Nevertheless, the absolute values of fluorescence lost in both types of nuclei were very similar. After extraction in 0.35 M NaCl, thymocyte nuclei displayed slightly greater fluorescence than control thymocyte nuclei, while the total fluorescence of hepatocyte nuclei declined. In hepatocyte nuclei extracted with TCA, with and without treatment with 0.35 M NaCl, two populations of diploid nuclei were apparent: one corresponding to parenchymal cell nuclei and the other comprised of non-parenchymal cell nuclei. Only single diploid populations were visible in acid-extracted material. The ratios of 4c2c, 8c4c, and 8c2c hepatocyte nuclei in control, acid-extracted, and NaCl-extracted groups were generally lower than the expected 224 values. These results indicate that total nuclear histones may be estimated microfluorometrically by computing the difference between acid-extracted and unextracted preparations treated in otherwise equivalent ways. In addition, despite very similar absolute losses of fluorescence after removal of histones in thymocyte and 2c hepatocyte nuclei, the proportion of total protein ascribable to histones is much greater in thymocyte nuclei than in 2c hepatocyte nuclei — or, conversely, the percentage of total protein attributable to non-histone proteins is much greater in 2c hepatocyte nuclei than in thymocyte nuclei.     

Sister kinetochore recapture in fission yeast occurs by two distinct mechanisms, both requiring Dam1 and Klp2

In eukaryotic cells, proper formation of the spindle is necessary for successful cell division. We have studied chromosome recapture in the fission yeast Schizosaccharomyces pombe. We show by live cell analysis that lost kinetochores interact laterally with intranuclear microtubules (INMs) and that both microtubule depolymerization (end-on pulling) and minus-end-directed movement (microtubule sliding) contribute to chromosome retrieval to the spindle pole body (SPB). We find that the minus-end-directed motor Klp2 colocalizes with the kinetochore during its transport to the SPB and contributes to the effectiveness of retrieval by affecting both end-on pulling and lateral sliding. Furthermore, we provide in vivo evidence that Dam1, a component of the DASH complex, also colocalizes with the kinetochore during its transport and is essential for its retrieval by either of these mechanisms. Finally, we find that the position of the unattached kinetochore correlates with the size and orientation of the INMs, suggesting that chromosome recapture may not be a random process.     

Effect of endurance training and chronic isoproterenol treatment on skeletal muscle sensitivity to norepinephrine

The purpose of this study was to determine the influence of metabolic stresses, such as endurance training and chronic isoproterenol treatment, on skeletal muscle sensitivity to norepinephrine. Using an isolated perfused rat hindlimb preparation, dose-response curves for skeletal muscle oxygen consumption (VO2) and vascular resistance were obtained with control, endurance trained, and isoproterenol treated rats. No significant difference was found between control and experimental groups for non-stimulated VO2. In response to NE infusion, trained rats showed a significantly greater increase in VO2 compared to control rats while the response of the isoproterenol treated rats was of the same magnitude as the one for their respective control rats. At the highest dose of NE infused, the vasopressor response was significantly lower in trained rats compared to control rats. At none of the doses was there a significant difference in the vasopressor response between control and isoproterenol treated rats. These results suggest that repeated exposures to high levels of catecholamines, as produced during endurance training, leads to an increased sensitivity of skeletal muscle to the effect of norepinephrine.