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- Schael, S, et al.
(författare)
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Precision electroweak measurements on the Z resonance
- 2006
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Ingår i: Physics Reports. - : Elsevier BV. - 0370-1573 .- 1873-6270. ; 427:5-6, s. 257-454
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Forskningsöversikt (refereegranskat)abstract
- We report on the final electroweak measurements performed with data taken at the Z resonance by the experiments operating at the electron-positron colliders SLC and LEP. The data consist of 17 million Z decays accumulated by the ALEPH, DELPHI, L3 and OPAL experiments at LEP, and 600 thousand Z decays by the SLID experiment using a polarised beam at SLC. The measurements include cross-sections, forward-backward asymmetries and polarised asymmetries. The mass and width of the Z boson, m(Z) and Gamma(Z), and its couplings to fermions, for example the p parameter and the effective electroweak mixing angle for leptons, are precisely measured: m(Z) = 91.1875 +/- 0.0021 GeV, Gamma(Z) = 2.4952 +/- 0.0023 GeV, rho(l) = 1.0050 +/- 0.0010, sin(2)theta(eff)(lept) = 0.23153 +/- 0.00016. The number of light neutrino species is determined to be 2.9840 +/- 0.0082, in agreement with the three observed generations of fundamental fermions. The results are compared to the predictions of the Standard Model (SM). At the Z-pole, electroweak radiative corrections beyond the running of the QED and QCD coupling constants are observed with a significance of five standard deviations, and in agreement with the Standard Model. Of the many Z-pole measurements, the forward-backward asymmetry in b-quark production shows the largest difference with respect to its SM expectation, at the level of 2.8 standard deviations. Through radiative corrections evaluated in the framework of the Standard Model, the Z-pole data are also used to predict the mass of the top quark, m(t) = 173(+10)(+13) GeV, and the mass of the W boson, m(W) = 80.363 +/- 0.032 GeV. These indirect constraints are compared to the direct measurements, providing a stringent test of the SM. Using in addition the direct measurements of m(t) and m(W), the mass of the as yet unobserved SM Higgs boson is predicted with a relative uncertainty of about 50% and found to be less than 285 GeV at 95% confidence level. (c) 2006 Elsevier B.V. All rights reserved.
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- Dai, JY, et al.
(författare)
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Conformational cycling in beta-phosphoglucomutase catalysis: Reorientation of the beta-D-glucose 1,6-(bis) phosphate intermediate
- 2006
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Ingår i: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 45:25, s. 7818-7824
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Tidskriftsartikel (refereegranskat)abstract
- Activated Lactococcus lactis beta-phosphoglucomutase (beta PGM) catalyzes the conversion of beta-D-glucose 1-phosphate (beta G1P) derived from maltose to beta-D-glucose 6-phosphate (G6P). Activation requires Mg2+ binding and phosphorylation of the active site residue Asp8. Initial velocity techniques were used to define the steady-state kinetic constants k(cat) = 177 +/- 9 s(-1), K-m = 49 +/- 4 mu M for the substrate, beta G1P and K-m = 6.5 +/- 0.7 mu M for the activator beta-D-glucose 1,6-bisphosphate (beta G1,6bisP). The observed transient accumulation of [C-14]beta G1,6bisP (12% at similar to 0.1 s) in the single turnover reaction carried out with excess beta PGM (40 mu M) and limiting [C-14]beta G1P (5 mu M) and beta G1,6bisP (5 mu M) supported the role of beta G1,6bisP as a reaction intermediate in the conversion of the, G1P to G6P. Single turnover reactions of [C-14]beta G1,6bisP with excess, beta PGM were carried out to demonstrate that phosphoryl transfer rather than ligand binding is rate-limiting and to show that the beta G1,6bisP binds to the active site in two different orientations (one positioning the C(1) phosphoryl group for reaction with Asp8, and the other orientation positioning the C(6) phosphoryl group for reaction with Asp8) with roughly the same efficiency. Single turnover reactions carried out with beta PGM, [C-14]beta G1P, and unlabeled beta G1,6bisP demonstrated complete exchange of label to the beta G1,6bisP during the catalytic cycle. Thus, the reorientation of the beta G1,6bisP intermediate that is required to complete the catalytic cycle occurs by diffusion into solvent followed by binding in the opposite orientation. Published X-ray structures of beta G1P suggest that the reorientation and phosphoryl transfer from beta G1,6bisP occur by conformational cycling of the enzyme between the active site open and closed forms via cap domain movement. Last, the equilibrium ratio of beta G1,6bisP to beta G1P plus G6P was examined to evidence a significant stabilization of beta PGM aspartyl phosphate.
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