919 research outputs found
Multiple hadron production in e+e- annihilation induced by heavy primary quarks. New analysis
In this paper we present an analysis of the multiple hadron production
induced by primary heavy quarks in e+e- annihilation with the account of most
complete and corrected experimental data. In the framework of perturbative QCD,
new theoretical bounds on the asymptotically constant differences of the
multiplicities in processes with light and heavy quarks are given.Comment: 26 pages, 7 figures, to be published in Particles & Nucle
The Schwinger Nonet Mass and Sakurai Mass-Mixing Angle Formulae Reexamined
We study the origins of the inaccuracies of Schwinger's nonet mass, and the
Sakurai mass-mixing angle, formulae for the pseudoscalar meson nonet, and
suggest new versions of them, modified by the inclusion of the pseudoscalar
decay constants. We use these new formulae to determine the pseudoscalar decay
constants and mixing angle. The results obtained, f_8/f_\pi =1.185\pm 0.040,
f_9/f_\pi =1.095\pm 0.020, f_\eta /f_\pi =1.085\pm 0.025, f_{\eta ^{'}}/f_\pi
=1.195\pm 0.035, \theta =(-21.4\pm 1.0)^o, are in excellent agreement with
experiment.Comment: 17 pages, LaTe
Charged Particle Multiplicity in Diffractive Deep Inelastic Scattering
The recent data from H1 Collaboration on hadron multiplicity in diffractive
DIS has been studied in the framework of perturbative QCD as a function of
invariant diffractive mass. The formulas obtained explain the observed excess
of particle production in diffractive DIS relative to that in DIS and
annihilation. It is shown that the results are sensitive to the quark--gluon
structure of the Pomeron. Namely, the data say in favour of a super-hard gluon
distribution at the initial scale.Comment: 12 pages, 3 figures; to be published in Phys. Rev.
Radion production in exclusive processes at CERN LHC
In the Randall-Sundrum (RS) scenario the compactification radius of the extra
dimension is stabilized by the radion, which is a scalar field lighter than the
graviton Kaluza-Klein states. It implies that the detection of the radion will
be the first signature of the stabilized RS model. In this paper we study the
exclusive production of the radion in electromagnetic and diffractive hadron -
hadron collisions at the LHC. Our results demonstrate that the diffractive
production of radion is dominant and should be feasible of study at CERN LHC.Comment: 6 pages, 3 figures, 1 tabl
Pseudoscalar Glueball, eta'-meson and its Excitation in the Chiral Effective Lagrangian
A generalization of the chiral effective lagrangian of order is
proposed which involves the -meson, its excitation, and the pseudoscalar
(PS) glueball. Model-independent constraints are found for the contributions to
the lagrangian of the above singlet states. Those allow one to independently
identify the nature of these singlet states in the framework of the approach.
The mixing among the iso-singlet states (including -state) is analysed,
and the hierarchy of the mixing angles is described which is defined by the
chiral and large- expansions. The recent PCAC results are reproduced,
which are related to the problem of the renormalization-group invariant
description of the and the PS glueball, and a further analysis of this
problem is performed.Comment: 19 pages LaTeX, no figures. Revised version accepted in Phis.Rev.
In Vitro Reconstitution of Eukaryotic Translation Reveals Cooperativity between Release Factors eRF1 and eRF3
SummaryEukaryotic translation termination is triggered by peptide release factors eRF1 and eRF3. Whereas eRF1 recognizes all three termination codons and induces hydrolysis of peptidyl tRNA, eRF3's function remains obscure. Here, we reconstituted all steps of eukaryotic translation in vitro using purified ribosomal subunits; initiation, elongation, and termination factors; and aminoacyl tRNAs. This allowed us to investigate termination using pretermination complexes assembled on mRNA encoding a tetrapeptide and to propose a model for translation termination that accounts for the cooperative action of eRF1 and eRF3 in ensuring fast release of nascent polypeptide. In this model, binding of eRF1, eRF3, and GTP to pretermination complexes first induces a structural rearrangement that is manifested as a 2 nucleotide forward shift of the toeprint attributed to pretermination complexes that leads to GTP hydrolysis followed by rapid hydrolysis of peptidyl tRNA. Cooperativity between eRF1 and eRF3 required the eRF3 binding C-terminal domain of eRF1
Negative cooperativity in adenylate formation catalysed by beef pancreas tryptophanyl-tRNA synthetase Influence of tRNATrp
Extended peptide-based inhibitors efficiently target the proteasome and reveal overlapping specificities of the catalytic β-subunits
AbstractBackground: The 26S proteasome is responsible for most cytosolic proteolysis, and is an important protease in major histocompatibility complex class I-mediated antigen presentation. Constitutively expressed proteasomes from mammalian sources possess three distinct catalytically active species, β1, β2 and β5, which are replaced in the γ-interferon-inducible immunoproteasome by a different set of catalytic subunits, β1i, β2i and β5i, respectively. Based on preferred cleavage of short fluorogenic peptide substrates, activities of the proteasome have been assigned to individual subunits and classified as ‘chymotryptic-like’ (β5), ‘tryptic-like’ (β2) and ‘peptidyl-glutamyl peptide hydrolyzing’ (β1). Studies with protein substrates indicate a far more complicated, less strict cleavage preference. We reasoned that inhibitors of extended size would give insight into the extent of overlapping substrate specificity of the individual activities and subunits.Results: A new class of proteasome inhibitors, considerably extended in comparison with the commonly used fluorescent substrates and peptide-based inhibitors, has been prepared. Application of the safety catch resin allowed the generation of the target compounds using a solid phase protocol. Evaluation of the new compounds revealed a set of highly potent proteasome inhibitors that target all individual active subunits with comparable affinity, unlike the other inhibitors described to date. Modification of the most active compound, adamantane-acetyl-(6-aminohexanoyl)3-(leucinyl)3-vinyl-(methyl)-sulfone (AdaAhx3L3VS), itself capable of proteasome inhibition in living cells, afforded a new set of radio- and affinity labels.Conclusions: N-terminal extension of peptide vinyl sulfones has a profound influence on both their efficiency and selectivity as proteasome inhibitors. Such extensions greatly enhance inhibition and largely obliterate selectivity towards the individual catalytic activities. We conclude that for the interaction with larger substrates, there appears to be less discrimination of different substrate sequences for the catalytic activities than is normally assumed based on the use of small peptide-based substrates and inhibitors. The compounds described here are readily accessible synthetically, and are more potent inhibitors in living cells than their shorter peptide vinyl sulfone counterparts
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