104 research outputs found
Specificity of cholera toxin and mono(ADP-ribosyl)transferase activity in cultured myoblasts
The relationship between ADP-ribosylation and phosphorylation using a model substrate, the specificity requirements for cholera toxin-catalyzed ADP-ribosylation using peptide substrates, and the role of ADP-ribosylation reactions in skeletal muscle were studied;Cholera toxin preferentially ADP-ribosylates the first arginyl residue of kemptide (Leu-Arg-Arg-Ala-Ser-Leu-Gly) and some ADP-ribosylation was observed on the second arginyl residue. A di(ADP-ribosyl)ated product was also formed. Phosphorylated seryl residue of kemptide decreased the extent of ADP-ribosylation of the arginyl residues by cholera toxin and mono(ADP-ribosyl)ated kemptide was a poor substrate for the cAMP-dependent protein kinase. Di(ADP-ribosyl)ated kemptide was not phosphorylated at all. These results suggest a possible relationship between ADP-ribosylation and phosphorylation;Synthetic peptides containing two arginyl groups with sequences derived from the GTP-binding proteins, Gs[alpha], T[alpha], Gi[alpha], and Go[alpha], were ADP-ribosylated by cholera toxin preferentially at the second arginyl residue. The specificity seen in the intact proteins, Gs[alpha] and T[alpha], was not seen. Peptides from Gi[alpha] and Go[alpha] were equally ADP-ribosylated by cholera toxin even though the native proteins are not substrates. The specificity could not be induced by various solvents or by an endogenous ADP-ribosylation factor, ARF. These results suggest that the tertiary structure of the native protein is important in the specificity observed in intact proteins and that peptides with disordered structures are not specifically ADP-ribosylated;An inhibitor, meta-iodobenzylguanidine (MIBG), for arginine-specific mono(ADP-ribosyl)transferases reversibly inhibited both proliferation and differentiation of embryonic chick myoblasts grown in culture. Micromolar (30 [mu]M) concentrations of MIBG blocked fusion, differentiation-specific increase in phosphocreatine kinase activity, both DNA and protein accumulation, expression of muscle-specific protein, titin, and also decreased the total NAD levels. These finding suggest a possible role for mono(ADP-ribosyl)ation reactions in myogenesis
Search for charged Higgs decays of the top quark using hadronic tau decays
We present the result of a search for charged Higgs decays of the top quark,
produced in collisions at 1.8 TeV. When the charged
Higgs is heavy and decays to a tau lepton, which subsequently decays
hadronically, the resulting events have a unique signature: large missing
transverse energy and the low-charged-multiplicity tau. Data collected in the
period 1992-1993 at the Collider Detector at Fermilab, corresponding to
18.70.7~pb, exclude new regions of combined top quark and charged
Higgs mass, in extensions to the standard model with two Higgs doublets.Comment: uuencoded, gzipped tar file of LaTeX and 6 Postscript figures; 11 pp;
submitted to Phys. Rev.
Inclusive jet cross section in collisions at TeV
The inclusive jet differential cross section has been measured for jet
transverse energies, , from 15 to 440 GeV, in the pseudorapidity region
0.10.7. The results are based on 19.5 pb of data
collected by the CDF collaboration at the Fermilab Tevatron collider. The data
are compared with QCD predictions for various sets of parton distribution
functions. The cross section for jets with GeV is significantly
higher than current predictions based on O() perturbative QCD
calculations. Various possible explanations for the high- excess are
discussed.Comment: 8 pages with 2 eps uu-encoded figures Submitted to Physical Review
Letter
Measurement of Dijet Angular Distributions at CDF
We have used 106 pb^-1 of data collected in proton-antiproton collisions at
sqrt(s)=1.8 TeV by the Collider Detector at Fermilab to measure jet angular
distributions in events with two jets in the final state. The angular
distributions agree with next to leading order (NLO) predictions of Quantum
Chromodynamics (QCD) in all dijet invariant mass regions. The data exclude at
95% confidence level (CL) a model of quark substructure in which only up and
down quarks are composite and the contact interaction scale is Lambda_ud(+) <
1.6 TeV or Lambda_ud(-) < 1.4 TeV. For a model in which all quarks are
composite the excluded regions are Lambda(+) < 1.8 TeV and Lambda(-) < 1. 6
TeV.Comment: 16 pages, 2 figures, 2 tables, LaTex, using epsf.sty. Submitted to
Physical Review Letters on September 17, 1996. Postscript file of full paper
available at http://www-cdf.fnal.gov/physics/pub96/cdf3773_dijet_angle_prl.p
Search for New Particles Decaying to Dijets at CDF
We have used 106 pb^-1 of data collected with the Collider Detector at
Fermilab to search for new particles decaying to dijets. We exclude at the 95%
confidence level models containing the following new particles: axigluons and
flavor universal colorons with mass between 200 and 980 GeV/c, excited quarks
with mass between 80 and 570 GeV/c^2 and between 580 and 760 GeV/c^2, color
octet technirhos with mass between 260 and 480 GeV/c^2, W' bosons with mass
between 300 and 420 GeV/c^2, and E_6 diquarks with mass between 290 and 420
GeV/c^2.Comment: 18 pages, 4 figures, 1 table. Submitted to Physical Review D Rapid
Communications. Postscript file of paper is also available at
http://www-cdf.fnal.gov/physics/pub97/cdf3276_dijet_search_prd_rc.p
The currency ratio in Tanzania: an econometric analysis
This study tested some key hypotheses on the determinants
of the currency ratio in Tanzania. The econometric results suggest that real income is, as theorized, negatively related to and a significant determinant of the currency ratio in Tanzania. The estimated income elasticity coefficient, found to be far less than unity, suggests there is poor substitution between currency and demand deposits in Tanzania. The results also showed that expected inflation was negatively related to the currency ratio in Tanzania. While the structural adjustment programme was found to increase and shift upward the currency ratio function in Tanzania, the liberalization of the financial sector was found to shift decrease and shift downward the currency ratio function. Most institutional variables were
found to lack the expected sign and significance in explaining the currency ratio in Tanzania, probably because of inadequacy of the proxies used
ADP-ribosylation of arginine
Arginine adenosine-5âČ-diphosphoribosylation (ADP-ribosylation) is an enzyme-catalyzed, potentially reversible posttranslational modification, in which the ADP-ribose moiety is transferred from NAD+ to the guanidino moiety of arginine. At 540 Da, ADP-ribose has the size of approximately five amino acid residues. In contrast to arginine, which, at neutral pH, is positively charged, ADP-ribose carries two negatively charged phosphate moieties. Arginine ADP-ribosylation, thus, causes a notable change in size and chemical property at the ADP-ribosylation site of the target protein. Often, this causes steric interference of the interaction of the target protein with binding partners, e.g. toxin-catalyzed ADP-ribosylation of actin at R177 sterically blocks actin polymerization. In case of the nucleotide-gated P2X7 ion channel, ADP-ribosylation at R125 in the vicinity of the ligand-binding site causes channel gating. Arginine-specific ADP-ribosyltransferases (ARTs) carry a characteristic R-S-EXE motif that distinguishes these enzymes from structurally related enzymes which catalyze ADP-ribosylation of other amino acid side chains, DNA, or small molecules. Arginine-specific ADP-ribosylation can be inhibited by small molecule arginine analogues such as agmatine or meta-iodobenzylguanidine (MIBG), which themselves can serve as targets for arginine-specific ARTs. ADP-ribosylarginine specific hydrolases (ARHs) can restore target protein function by hydrolytic removal of the entire ADP-ribose moiety. In some cases, ADP-ribosylarginine is processed into secondary posttranslational modifications, e.g. phosphoribosylarginine or ornithine. This review summarizes current knowledge on arginine-specific ADP-ribosylation, focussing on the methods available for its detection, its biological consequences, and the enzymes responsible for this modification and its reversal, and discusses future perspectives for research in this field
Ratios of bottom meson branching fractions involving J/psi mesons and determination of b quark fragmentation fractions
We report a measurement of the ratios of the decay rates of the B^+, B^0 and
B^0_s mesons into exclusive final states containing a J/psi meson. The final
states were selected from 19.6 pb^{-1} of p-pbar collisions recorded by the
Collider Detector at Fermilab. These data are interpreted to determine the
bquark fragmentation fractions f_u, f_d and f_s. We also determine the
branching fractions for the decay modes B^+ --> J/psi K^+, B^+ --> J/psi
K^*(892)^+, B^0 --> J/psi K^0, B^0 --> J/psi K^*(892)^0 and B_s^0 --> J/psi
phi(1020). We discuss the implications of these measurements to B meson decay
models.Comment: 40 pages with 5 figures. Submitted to Phys. Rev. D. PostScript also
available at http://www-cdf.fnal.gov/physics/pub96/cdf3609_bfrag_br_prd.p
Further Properties of High-Mass Multijet Events at the Fermilab Proton-Antiproton Collider
The properties of high-mass multijet events produced at the Fermilab
proton-antiproton collider are compared with leading order QCD matrix element
predictions, QCD parton shower Monte Carlo predictions, and the predictions
from a model in which events are distributed uniformly over the available
multibody phase-space. Multijet distributions corresponding to (4N-4) variables
that span the N-body parameter space are found to be well described by the QCD
calculations for inclusive three-jet, four-jet, and five-jet events. The
agreement between data, QCD Matrix Element calculations, and QCD parton shower
Monte Carlo predictions suggests that 2 -> 2 scattering plus gluon radiation
provides a good first approximation to the full LO QCD matrix element for
events with three, four, or even five jets in the final state.Comment: 49 pages with 19 figures. Submitted to Phys. Rev. D. PostScript with
full resolution figures also available at
http://www-cdf.fnal.gov/physics/pub96/cdf3480_multijet_prd_draft3.p
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