Based on an integrated luminosity of 1.61 fb\(^{-1}\) \(e^+e^-\) collision data collected with the KLOE detector at DA\(\Phi\)NE, the Frascati \(\phi\)-factory, a search for the \(P\)- and ...\(CP\)-violating decay \(\eta\to\pi^{+}\pi^{-}\) has been performed. Radiative \(\phi\to\eta\gamma\) decay is exploited to access the \(\eta\) mesons. No signal is observed in the \(\pi^{+}\pi^{-}\) invariant mass spectrum, and the upper limit on the branching fraction at 90\% confidence level is determined to be \({\mathcal B}(\eta\to\pi^{+}\pi^{-})<4.9\times10^{-6}\), which is approximately three times smaller than the previous KLOE result. From the combination of these two measurements we get \({\mathcal B}(\eta\to\pi^{+}\pi^{-}) < 4.4\times10^{-6}\) at 90\% confidence level.
Based on a sample of 300 million \(K_S\) mesons produced in \(\phi \to K_L K_S\) decays recorded by the KLOE experiment at the DA\(\Phi\)NE \(e^+e^-\) collider we have measured the branching fraction ...for the decay \(K_S \to \pi \mu \nu\). The \(K_S\) mesons are identified by the interaction of \(K_L\) mesons in the detector. The \(K_S \to \pi \mu \nu\) decays are selected by a boosted decision tree built with kinematic variables and by a time-of-flight measurement. Signal efficiencies are evaluated with data control samples of \(K_L \to \pi \mu \nu\) decays. A fit to the reconstructed muon mass distribution finds \(7223 \pm 180\) signal events. Normalising to the \(K_S \to \pi^+ \pi^-\) decay events the result for the branching fraction is \(\mathcal{B}(K_S \to \pi \mu \nu) = (4.56 \pm 0.11_{\rm stat} \pm 0.17_{\rm syst})\times10^{-4}\).
The determination of low-energy cross sections and branching ratios of the K\(^-\) multi-nucleon absorption processes in \(\Lambda\)p and \(\Sigma^0\)p final states performed by the AMADEUS ...collaboration is presented. Low momentum K\(^-\) (\(p_\mathrm{K} \simeq\) 127 MeV/c) produced at the DA\(\Phi\)NE collider are impinged on a Carbon target within the KLOE detector and the two and three nucleon absorption processes are disentangled by comparing the experimental data to phenomenological calculations. The \(\Lambda\)p spectra are interpreted in terms of K\(^-\) multi-nucleon absorption processes; the possible contribution of a K\(^-\)pp bound state is demonstrated to overlap with the two nucleon capture process, its absolute yield thus resulting indistinguishable.
Using 1.63 fb\(^{-1}\) of integrated luminosity collected by the KLOE experiment about \(7\times 10^4\) \(K_S \rightarrow \pi^{\pm}e^{\mp}\nu\) decays have been reconstructed. The measured value of ...the charge asymmetry for this decay is \(A_S = (-4.9 \pm 5.7_{stat} \pm 2.6_{syst}) \times 10^{-3}\), which is almost twice more precise than the previous KLOE result. The combination of these two measurements gives \(A_S = (-3.8 \pm 5.0_{stat} \pm 2.6_{syst}) \times 10^{-3}\) and, together with the asymmetry of the \(K_L\) semileptonic decay, provides significant tests of the CPT symmetry. The obtained results are in agreement with CPT invariance.
We searched for the \(\mu^+\mu^-\) decay of a light vector gauge boson, also known as dark photon, in the \(e^+ e^- \to \mu^+ \mu^- \gamma_{\rm ISR}\) process by means of the Initial State Radiation ...(ISR) method. We used 1.93~fb\(^{-1}\) of data collected by the KLOE experiment at the DA\(\Phi\)NE \(\phi\)-factory. No structures have been observed over the irreducible \(\mu^+ \mu^-\) background. A 90\% CL limit on the ratio \(\varepsilon^2=\alpha^{\prime}/\alpha\) between the dark coupling constant and the fine structure constant of \( 3\times 10^{-6}-2\times 10^{-7}\) has been set in the dark photon mass region between 519 MeV and 973 MeV. This new limit has been combined with the published result obtained investigating the hypothesis of the dark photon decaying into hadrons in \(e^+ e^- \to \pi^+ \pi^- \gamma_{\rm ISR}\) events. The combined 90\% CL limit increases the sensitivity especially in the \(\rho-\omega\) interference region and excludes \(\varepsilon^2\) greater than \((13-2)\times 10^{-7}\). For dark photon masses greater than 600 MeV the combined limit is lower than 8~\(\times\, 10^{-7}\) resulting more stringent than present constraints from other experiments.
The three precision measurements of the cross section \(\sigma\big(e^+e^-\rightarrow\pi^+\pi^-\gamma(\gamma)\big)\) using initial state radiation by the KLOE collaboration provide an important input ...for the prediction of the hadronic contribution to the anomalous magnetic moment of the muon. These measurements are correlated for both statistical and systematic uncertainties and, therefore, the simultaneous use of these measurements requires covariance matrices that fully describe the correlations. We present the construction of these covariance matrices and use them to determine a combined KLOE measurement for \(\sigma\big(e^+e^-\rightarrow\pi^+\pi^-\gamma(\gamma)\big)\). We find, from this combination, a two-pion contribution to the muon magnetic anomaly in the energy range \(0.10 < s < 0.95\) GeV\(^2\) of \(a_{\mu}^{\pi^+\pi^-} = (489.8 \pm 1.7_{\rm stat} \pm 4.8_{\rm sys} ) \times 10^{-10}\).
Among protein residues, cysteines are one of the prominent candidates to ROS‐mediated and RNS‐mediated post‐translational modifications, and hydrogen peroxide (H2O2) is the main ROS candidate for ...inducing cysteine oxidation. The reaction with H2O2 is not common to all cysteine residues, being their reactivity an utmost prerequisite for the sensitivity towards H2O2. Indeed, only deprotonated Cys (i.e. thiolate form, S−) can react with H2O2 leading to sulphenic acid formation (SOH), which is considered as a major/central player of ROS sensing pathways. However, cysteine sulphenic acids are generally unstable because they can be further oxidized to irreversible forms (sulphinic and sulphonic acids, SO2H and SO3H, respectively), or alternatively, they can proceed towards further modifications including disulphide bond formation (SS), S‐glutathionylation (SSG) and sulphenamide formation (SN). To understand why and how cysteine residues undergo primary oxidation to sulphenic acid, and to explore the stability of cysteine sulphenic acids, a combination of biochemical, structural and computational studies are required. Here, we will discuss the current knowledge of the structural determinants for cysteine reactivity and sulphenic acid stability within protein microenvironments.
This review highlights the importance of acidity and nucleophilicity of protein cysteine thiols in determining the rate of H2O2‐mediated primary oxidation to sulphenic acids. The stability and reactivity of sulphenic acids is also investigated, being strictly correlated to the cysteine microenvironment and dependent upon structural determinants, which are specific of each protein sensitive to oxidation. These findings reinforce the prominent role of cysteine sulphenic acids in redox signalling, but a combination of biochemical, structural and computational approaches is mandatory to get insight into the kinetic and thermodynamics factors controlling cysteine oxidation.
Regulation of the Calvin-Benson cycle under varying light/dark conditions is a common property of oxygenic photosynthetic organisms and photosynthetic glyceraldehyde-3-phosphate dehydrogenase (GAPDH) ...is one of the targets of this complex regulatory system. In cyanobacteria and most algae, photosynthetic GAPDH is a homotetramer of GapA subunits which do not contain regulatory domains. In these organisms, dark-inhibition of the Calvin-Benson cycle involves the formation of a kinetically inhibited supramolecular complex between GAPDH, the regulatory peptide CP12 and phosphoribulokinase. Conditions prevailing in the dark, i.e. oxidation of thioredoxins and low NADP(H)/NAD(H) ratio promote aggregation. Although this regulatory system has been inherited in higher plants, these phototrophs contain in addition a second type of GAPDH subunits (GapB) resulting from the fusion of GapA with the C-terminal half of CP12. Heterotetrameric A₂B₂-GAPDH constitutes the major photosynthetic GAPDH isoform of higher plants chloroplasts and coexists with CP12 and A₄-GAPDH. GapB subunits of A₂B₂-GAPDH have inherited from CP12 a regulatory domain (CTE for C-terminal extension) which makes the enzyme sensitive to thioredoxins and pyridine nucleotides, resembling the GAPDH/CP12/PRK system. The two systems are similar in other respects: oxidizing conditions and low NADP(H)/NAD(H) ratios promote aggregation of A₂B₂-GAPDH into strongly inactivated A₈B₈-GAPDH hexadecamers, and both CP12 and CTE specifically affect the NADPH-dependent activity of GAPDH. The alternative, lower activity with NADH is always unaffected. Based on the crystal structure of spinach A₄-GAPDH and the analysis of site-specific mutants, a model of the autonomous (CP12-independent) regulatory mechanism of A₂B₂-GAPDH is proposed. Both CP12 and CTE seem to regulate different photosynthetic GAPDH isoforms according to a common and ancient molecular mechanism.
Based on a sample of 300 million K-S mesons produced in phi -> KLKS decays recorded by the KLOE experiment at the DA Phi NE e(+)e(-) collider we have measured the branching fraction for the decay ...K-S -> pi mu nu. The K-S mesons are identified by the interaction of K-L mesons in the detector. The K-S -> pi mu nu decays are selected by a boosted decision tree built with kinematic variables and by a time-of-flight measurement. Signal efficiencies are evaluated with data control samples of K-L -> pi mu nu decays. A fit to the reconstructed muon mass distribution finds 7223 +/- 180 signal events. Normalising to the K-S -> pi(+)pi(-) decay events the result for the branching fraction is B(K-S -> pi mu nu) = (4.56 +/- 0.11(stat) +/- 0.17(syst)) x 10(-4). It is the first measurement of this decay mode and the result allows an independent determination of vertical bar V-us vertical bar and a test of the lepton-flavour universality. (c) 2020 The Author. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
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