Amino acid oxidation of the D1 and D2 proteins by oxygen radicals during photoinhibition of Photosystem II

The Photosystem II reaction center is vulnerable to photoinhibition. The D1 and D2 proteins, lying at the core of the photosystem, are susceptible to oxidative modification by reactive oxygen species that are formed by the photosystem during illumination. Using spin probes and EPR spectroscopy, we have determined that both O2 -and HO are involved in the photoinhibitory process. Using tandem mass spectroscopy, we have identified a number of oxidatively modified D1 and D2 residues. Our analysis indicates that these oxidative modifications are associated with formation of HO at both the Mn4O5Ca cluster and the nonheme iron. Additionally, O2 -appears to be formed by the reduction of O2 at either PheoD1 or QA. Early oxidation of D1:332H,which is coordinatedwith theMn1 of the Mn4O5Ca cluster, appears to initiate a cascade of oxidative events that lead to the oxidative modification of numerous residues in the C termini of the D1 and D2 proteins on the donor side of the photosystem. Oxidation of D2:244Y, which is a bicarbonate ligand for the nonheme iron, induces the propagation of oxidative reactions in residues of the D-de loop of the D2 protein on the electron acceptor side of the photosystem. Finally, D1: 130E and D2: 246Mare oxidatively modified by O2 -formed by the reduction of O2 either by PheoD1 -or QA -. The identification of specific amino acid residues oxidized by reactive oxygen species provides insights into the mechanism of damage to the D1 and D2 proteins under light stress

Hacia una pedagogía como teoría crítica en la formación de profesores en Ciencias de la Educación

El presente trabajo parte de la siguiente pregunta: ¿Qué lugar ocupa hoy y cuál debería ocupar la Pedagogía en la formación de profesores en Ciencias de la Educación?; y en la búsqueda de una respuesta a esta pregunta surge a posteriori: ¿Se puede pensar la pedagogía como teoría crítica frente a las ciencias de la educación (entendidas como ciencias que producen “Teoría Tradicional”)? Porque si esto fuera así los pedagogos tendríamos la responsabilidad de pensar una teoría de la educación de carácter emancipatorio para poder replantear la cuestión de “¿Hacia dónde va la educación?” Es decir, si la pedagogía es un saber y una reflexión sobre la práctica, debemos poder producir un saber que sea emancipatorio y propositivo que nos permita decir como apuntar al objetivo de la igualdad en la escuela. Es fundamental replantear en la formación de profesionales de la educación ¿Qué es lo que hacemos como educadores?, ¿Qué sentido tiene nuestro trabajo docente? ¿Para qué educar hoy? Habría que repensar el rol de la pedagogía posicionándola como teoría crítica en la formación de profesores en Ciencias de la Educación, teniendo en cuenta este marco actual que se nos presenta.Facultad de Humanidades y Ciencias de la Educació

Genomics-based phylogenetic and population genetic analysis of global samples confirms Halophila johnsonii Eiseman as Halophila ovalis (R.Br.) Hook.f.

Halophila johnsonii is an endangered seagrass species that is restricted to the southeast coast of Florida, United States. Its taxonomic status has been called into question, in particular, given the close morphological and genetic similarity of H. johnsonii and the widely distributed and morphologically variable Halophila ovalis, which is largely restricted to the Indo-Pacific region. While a close relationship to H. ovalis is uncontroversial, it remains uncertain whether H. johnsonii represents a distinct lineage or is a recent introduction to the Florida region. Given the conservation status of H. johnsonii, distinguishing these alternatives has important implications for the management of the species and its habitat. Here, we develop molecular data sets for samples of H. johnsonii and H. ovalis including DNA sequences, genome-wide SNPs and microsatellites with the view to resolving the affinities of H. johnsonii with respect to the wider H. ovalis complex. Phylogenetic hypotheses based upon plastid (∼18000 bp) and low copy nuclear DNA (∼6500 bp) sequences derived from hybrid capture, along with 990 genome-wide ddRAD SNPs consistently resolved H. johnsonii within H. ovalis. Specifically, we found a close affinity between H. johnsonii and H. ovalis sampled from the east coast of Africa. In addition, Halophila specimens collected in Antigua, which are within the range of morphological variation typical for H. ovalis, are virtually identical to H. johnsonii and the East African H. ovalis samples based upon DNA sequence analyses and these group together using Bayesian clustering analyses of microsatellites and ddRAD SNPs. We conducted population genetic analyses using large number of H. johnsonii samples collected over a 17-year period. Genotypic data generated through microsatellites and ddRAD SNPs revealed genetic uniformity for all 132 H. johnsonii samples across the Indian River Lagoon, Florida, while samples of H. ovalis from Antigua shared the same genotype as H. johnsonii. We conclude that the lack of genetic diversity and the absence of sexual reproduction strongly indicates that the total range of H. johnsonii is actually one clone that is closely related to populations in Africa and Antigua and may be derived from a recent introduction from one of those regions.Michelle Waycott, Kor-jent van Dijk, Ainsley Calladine, Eric Bricker and Ed Biffi

One-step isolation and biochemical characterization of a highlyactive plant PSII monomeric core

We describe a one-step detergent solubilization protocol for isolating a highly active form of Photosystem II (PSII) from Pisum sativum L. Detailed characterization of the preparation showed that the complex was a monomer having no light harvesting proteins attached. This core reaction centre complex had, however, a range of low molecular mass intrinsic proteins as well as the chlorophyll binding proteins CP43 and CP47 and the reaction centre proteins D1 and D2. Of particular note was the presence of a stoichiometric level of PsbW, a low molecular weight protein not present in PSII of cyanobacteria. Despite the high oxygen evolution rate, the core complex did not retain the PsbQ extrinsic protein although there was close to a full complement of PsbO and PsbR and partial level of PsbP. However, reconstitution of PsbP and PsbPQ was possible. The presence of PsbP in absence of LHCII and other chlorophyll a/b binding proteins confirms that LHCII proteins are not a strict requirement for the assembly of this extrinsic polypeptide to the PSII core in contrast with the conclusion of Caffarri et al. (2009)

Search for Light Gluinos via the Spontaneous Appearance of pi+pi- Pairs with an 800 GeV/c Proton Beam at Fermilab

We searched for the appearance of pi+pi- pairs with invariant mass greater than 648 MeV in a neutral beam. Such an observation could signify the decay of a long-lived light neutral particle. We find no evidence for this decay. Our null result severely constrains the existence of an R0 hadron, which is the lightest bound state of a gluon and a light gluino, and thereby also the possibility of a light gluino. Depending on the photino mass, we exclude the R0 in the mass and lifetime ranges of 1.2 -- 4.6 GeV and 2E-10 -- 7E-4 seconds, respectively. (To Appear in Phys. Rev. Lett.)Comment: Documentstyle aps,epsfig,prl (revtex), 6 pages, 7 figure

Formic Acid Free Flowsheet Development To Eliminate Catalytic Hydrogen Generation In The Defense Waste Processing

The Defense Waste Processing Facility (DWPF) processes legacy nuclear waste generated at the Savannah River Site (SRS) during production of plutonium and tritium demanded by the Cold War. The nuclear waste is first treated via a complex sequence of controlled chemical reactions and then vitrified into a borosilicate glass form and poured into stainless steel canisters. Converting the nuclear waste into borosilicate glass canisters is a safe, effective way to reduce the volume of the waste and stabilize the radionuclides. Testing was initiated to determine whether the elimination of formic acid from the DWPF's chemical processing flowsheet would eliminate catalytic hydrogen generation. Historically, hydrogen is generated in chemical processing of alkaline High Level Waste sludge in DWPF. In current processing, sludge is combined with nitric and formic acid to neutralize the waste, reduce mercury and manganese, destroy nitrite, and modify (thin) the slurry rheology. The noble metal catalyzed formic acid decomposition produces hydrogen and carbon dioxide. Elimination of formic acid by replacement with glycolic acid has the potential to eliminate the production of catalytic hydrogen. Flowsheet testing was performed to develop the nitric-glycolic acid flowsheet as an alternative to the nitric-formic flowsheet currently being processed at the DWPF. This new flowsheet has shown that mercury can be reduced and removed by steam stripping in DWPF with no catalytic hydrogen generation. All processing objectives were also met, including greatly reducing the Slurry Mix Evaporator (SME) product yield stress as compared to the baseline nitric/formic flowsheet. Ten DWPF tests were performed with nonradioactive simulants designed to cover a broad compositional range. No hydrogen was generated in testing without formic acid

Theoretical studies of the historical development of the accounting discipline: a review and evidence

Many existing studies of the development of accounting thought have either been atheoretical or have adopted Kuhn's model of scientific growth. The limitations of this 35-year-old model are discussed. Four different general neo-Kuhnian models of scholarly knowledge development are reviewed and compared with reference to an analytical matrix. The models are found to be mutually consistent, with each focusing on a different aspect of development. A composite model is proposed. Based on a hand-crafted database, author co-citation analysis is used to map empirically the entire literature structure of the accounting discipline during two consecutive time periods, 1972–81 and 1982–90. The changing structure of the accounting literature is interpreted using the proposed composite model of scholarly knowledge development

Light Gluino Search for Decays Containing pi+pi- or pi0 from a Neutral Hadron Beam at Fermilab

We report on two null searches, one for the spontaneous appearance of $\pi^+\pi^-$ pairs, another for a single $\pi^0$, consistent with the decay of a long-lived neutral particle into hadrons and an unseen neutral particle. For the lowest level gluon-gluino bound state, known as the $R^0$, we exclude the decays $R^0\to \pi^+\pi^-\tilde{\gamma}$ and $R^0\to \pi^0\tilde{\gamma}$ for the masses of $R^0$ and $\tilde{\gamma}$ in the theoretically allowed range. In the most interesting $R^0$ mass range, $\leq 3 GeV/c^2$, we exclude $R^0$ lifetimes from $3\times 10^{-10}$ seconds to as high as $10^{-3}$ seconds, assuming perturbative QCD production for the $R^0$.Comment: 15 pages, 7 figure

Control of intestinal stem cell function and proliferation by mitochondrial pyruvate metabolism.

Most differentiated cells convert glucose to pyruvate in the cytosol through glycolysis, followed by pyruvate oxidation in the mitochondria. These processes are linked by the mitochondrial pyruvate carrier (MPC), which is required for efficient mitochondrial pyruvate uptake. In contrast, proliferative cells, including many cancer and stem cells, perform glycolysis robustly but limit fractional mitochondrial pyruvate oxidation. We sought to understand the role this transition from glycolysis to pyruvate oxidation plays in stem cell maintenance and differentiation. Loss of the MPC in Lgr5-EGFP-positive stem cells, or treatment of intestinal organoids with an MPC inhibitor, increases proliferation and expands the stem cell compartment. Similarly, genetic deletion of the MPC in Drosophila intestinal stem cells also increases proliferation, whereas MPC overexpression suppresses stem cell proliferation. These data demonstrate that limiting mitochondrial pyruvate metabolism is necessary and sufficient to maintain the proliferation of intestinal stem cells