Identification of the structure of large-scale MHD perturbations in a tokamak from Mirnov signals

An algorithm is proposed that allows one to identify the MHD mode structure in toroidal plasmas by processing signals from Mirnov probes measuring plasma MHD activity. The algorithm differs fundamentally from the diagnostic methods presently used in tokamaks, being simpler and more efficient. The algorithm is based on constructing an analytic signal using the Hilbert transformation of the Mirnov signals at a given instant. The phase and amplitude dependences obtained take into account the toroidal effects and allow one to determine the number and amplitude of the excited MHD mode. The algorithm was approbated with both test signals and actual signals from MHD diagnostics in the T-10 tokamak. It is demonstrated that the algorithm can be used to analyze single-mode MHD instabilities in toroidal plasmas.     

Phenotypic variation and stress resistance in core and peripheral populations of Hordeum spontaneum

The phenotypic variation and response of plants to water stress were studied in a field trial in populations of wild barley, Hordeum spontaneum Koch. from Israel and Turkmenistan. Populations from the species distributional core and periphery were compared and contrasted for phenotypic variation in 16 phenological and morphological traits. The peripheral populations (six) were found to be phenotypically more variable and more resistant to water stress than core populations (12). The association of water-stress resistance with high phenotypic variability gives support to the hypothesis that populations that are genetically more variable are better adapted or pre-adapted to environmental changes and are thus valuable for conservation.     

A bioluminescence method for direct measurement of phosphodiesterase activity

We have adapted bioluminescence methods to be able to measure phosphodiesterase (PDE) activity in a one-step technique. The method employs a four-enzyme system (PDE, adenylate kinase (AK) using excess CTP instead of ATP as substrate, pyruvate kinase (PK), and firefly luciferase) to generate ATP, with measurement of the concomitant luciferase-light emission. Since AK, PK, and luciferase reactions are coupled to recur in a cyclic manner, AMP recycling maintains a constant rate of ATP formation, proportional to the steady-state AMP concentration. The cycle can be initiated by the PDE reaction that yields AMP. As long as the PDE reaction is rate limiting, the system is effectively at steady state and the bioluminescence kinetics progresses at a constant rate proportional to the PDE activity. In the absence of cAMP and PDE, low concentrations of AMP trigger the AMP cycling, which allows standardizing the system. The sensitivity of the method enables detection of <1 μU (pmol/min) of PDE activity in cell extracts containing 0.25–10 μg protein. Assays utilizing pure enzyme showed that 0.2 mM IBMX completely inhibited PDE activity. This single-step enzyme- and substrate-coupled cyclic-reaction system yields a simplified, sensitive, reproducible, and accurate method for quantifying PDE activities in small biological samples.     

Physical and functional interaction between Pes1 and Bop1 in mammalian ribosome biogenesis

Molecular mechanisms of mammalian ribosome biogenesis remain largely unexplored. Here we develop a series of transposon-derived dominant mutants of Pes1, the mouse homolog of the zebrafish Pescadillo and yeast Nop7p implicated in ribosome biogenesis and cell proliferation control. Six Pes1 mutants selected by their ability to reversibly arrest the cell cycle also impair maturation of the 28S and 5.8S rRNAs in mouse cells. We show that Pes1 physically interacts with the nucleolar protein Bop1, and both proteins direct common pre-rRNA processing steps. Interaction with Bop1 is essential for the efficient incorporation of Pes1 into nucleolar preribosomal complexes. Pes1 mutants defective for the interaction with Bop1 lose the ability to affect rRNA maturation and the cell cycle. These data show that coordinated action of Pes1 and Bop1 is necessary for the biogenesis of 60S ribosomal subunits.     

N-terminal sequences direct the autophosphorylation states of the FER tyrosine kinases in vivo

p94(fer) and p51(ferT) are two tyrosine kinases which share identical SH2 and kinase domains but differ in their N-terminal regions. While p94(fer) is expressed in most mammalian cells, the accumulation of p51(ferT) is restricted to meiotic spermatocytes. Here we show that the different N-terminal tails of p94(fer) and p51(ferT) direct different autophosphorylation states of these two kinases in vivo. N-terminal coiled-coil domains cooperated to drive the oligomerization and autophosphorylation in trans of p94(fer). Moreover, the ectopically expressed N-terminal tail of p94(fer) could act as a dominant negative mutant and associated with the endogenous p94(fer) protein in CHO cells. This increased significantly the percentage of cells residing in the G0/G1 phase, thus suggesting a role for p94(fer) in the regulation of G1 progression. Unlike p94(fer), overexpressed p51(ferT) was not autophosphorylated in COS1 cells. However, removal of the unique N-terminal 43 aa of p51(ferT) or the replacement of this region by a parallel segment from p94(fer) endowed the modified p51(ferT) with the ability to autophosphorylate. The unique N-terminal sequences of p51(ferT) thus interfere with its ability to autophosphorylate in vivo. These experiments indicate that the N-terminal sequences of the FER tyrosine kinases direct their different cellular autophosphorylation states, thereby dictating their different cellular functions.     

CC chemokine receptor-3 (CCR3) antagonists: improving the selectivity of DPC168 by reducing central ring lipophilicity

DPC168, a benzylpiperidine-substituted aryl urea CCR3 antagonist evaluated in clinical trials, was a relatively potent inhibitor of the 2D6 isoform of cytochrome P-450 (CYP2D6). Replacement of the cyclohexyl central ring with saturated heterocycles provided potent CCR3 antagonists with improved selectivity against CYP2D6. The favorable preclinical profile of DPC168 was maintained in an acetylpiperidine derivative, BMS-570520.     

Characterization of Porins Isolated from the Outer Membrane of Serratia liquefaciens

A major outer membrane protein with an apparent molecular weight of 42 kDa was purified from Serratia liquefaciens grown on Brain Heart Infusion medium. The same protein was obtained when the cells were grown on a synthetic medium supplemented with 2% glucose. The amino acid composition of this protein revealed it to be hydrophilic. The pore-forming ability of the 42-kDa protein was determined by the liposome swelling assay. This assay demonstrated that the protein forms nonspecific channels with a diameter between 1.16 and 1.6 nm. An additional protein with a molecular weight of 47 kDa was obtained on synthetic medium supplemented with maltose. This protein exhibited specific pore-forming ability to maltose and maltodextrins, but was also permeable to other compounds, according to their size. When bacteria were grown on Nutrient Broth medium, two outer membrane proteins with molecular weights of 41 kDa and 42 kDa were produced by the bacteria. All three types of proteins represent monomers of respective oligomers. The monomers did not exhibit pore-forming ability when incorporated into liposomes. We, therefore, propose that the oligomer is the functional unit of a porin capable of forming permeability channels in the outer membrane of Serratia liquefaciens. These results indicate that S. liquefaciens contains several porins exhibiting specific osmoregulation or that are induced by a specific nutrient, where the 42-kDa outer membrane protein of this bacterium is certainly a major porin. Received: 6 July 1998 / Accepted: 19 August 1998     

Testosterone regulates 25-hydroxycholesterol production in testicular macrophages

Recently, we found that testicular macrophages produce 25-hydroxycholesterol (25-HC) and express 25-hydroxylase, the enzyme that converts cholesterol to 25-HC. In addition, 25-HC may be an important paracrine factor mediating the known interactions between macrophages and neighboring Leydig cells, because it is efficiently converted to testosterone by Leydig cells. The purpose of the present study was to determine if testosterone can regulate the production of 25-HC in rat testicular macrophages, representing a potential negative-feedback loop from Leydig cells. We found that expression of 25-hydroxylase mRNA and production of 25-HC by cultured testicular macrophages were significantly inhibited by testosterone at 10 micro g/ml. This dose of testosterone did not have an effect on cell viability and did not change the rate of mRNA degradation in the presence of actinomycin D. These studies indicate that production of 25-HC is negatively regulated by testosterone, which may be representative of a paracrine negative-feedback loop.     

N-Arylalkylpiperidine urea derivatives as CC chemokine receptor-3 (CCR3) antagonists

The synthesis and structure-activity relationships of N-arylalkylpiperidylmethyl ureas as antagonists of the CC chemokine receptor-3 (CCR3) are presented. These compounds displayed potent binding to the receptor as well as functional antagonism of eotaxin-elicited effects on eosinophils.