Mechanistic enzymology of CO dehydrogenase from Clostridium thermoaceticum

The final steps in acetyl-CoA biosynthesis by anaerobic bacteria are performed by carbon monoxide dehydrogenase (CODH), a nickel/iron-sulfur protein. An important achievement was to establish conditions under which acetyl-CoA synthesis by purified enzymes equals the in vivo rate of acetate synthesis. Under these optimized conditions we established that the rate limiting step in the synthesis of acetyl-CoA from methyl-H[sub 4]folate, CO and CoA is likely to be the methylation of CODH by the methylated corrinoid/iron-sulfur protein. We then focused on stopped flow studies of this rate limiting transmethylation reaction and established its mechanism. We have studied the carbonylation of CODH by infrared and resonance Raman spectroscopy and determined that the [Ni-Fe[sup 3-4]S[sub 4]]-CO species which has been characterized by magnetic resonance methods can be described as [Ni-X-Fe[sub 3-4]S[sub 4]]-C[equivalent to]O. We showed that this species is the catalytically competent precursor of the carbonyl group of acetyl-CoA. We have made progress in the synthesis of seleno-coenzyme A, which we will use to probe the binding of CoA to CODH. We also have compared the CODH from Methanosarcina thermophila with the C. thermoaceticum enzyme by EPR and electrochemical methods and found that the metal sites of these enzymes are remarkably similar given the evolutionary separation between archaea and bacteria domains

Bullying y rendimiento académico de los alumnos de educación secundaria de la I:E Santa Rosa de Lima Cabracancha- Chota 2015

El estudio titulado “Bullying y rendimiento académico de los alumnos de educación secundaria de la I. E. Santa Rosa de Lima Cabracancha – Chota, 2015” tuvo como objetivo determinar la relación entre bullying y rendimiento académico de los alumnos de educación secundaria. Estudio de enfoque cuantitativa, de tipo descriptiva, no experimental, diseño transversal y correlacional. La muestra estuvo conformada por 97 alumnos. Se utilizó un cuestionario de 12 preguntas sobre las características socioeconómicas y familiares, la escala índice global del bullying de Chávez, C y Delgado, F. (2013) y ficha de rendimiento académico. Como resultados tenemos que los alumnos se encuentran entre la edad de 12 a 14 años (47,4%), predominando las mujeres con el 52,6%, los grados de estudios con más altos porcentajes están primero, segundo y tercero con 22,7% respectivamente, el 44,3%, proceden del caserío de Cabracancha, pertenece a la religión católica (88,7%) y provienen de familias nucleares (73,2%), el 73,2% de los padres son casados, el 67% se dedican a la agricultura y tienen primaria incompleta (48,5%). En cuanto a las madres de los alumnos el 95,9% son amas de casa, el 50,5% tienen grado de instrucción primaria incompleta; el 68% de las familias cuentan con ingreso económico mensual menor de 750 soles. En cuanto al bullying el 99% sufren de bullying medio, el 1% sufre de bullying alto. Respecto al rendimiento académico el 39,2% se encontró en la categoría medio y el 1,0% en deficiente. Estos resultados permitieron contrastar la hipótesis nula que no existe relación entre el bullying y el rendimiento académico a un nivel de significancia del 5% con un valor p = 0.581. Se concluye que existe la presencia de bullying pero no hay relación con el rendimiento académico.Tesi

Enzymology of acetoclastic methanogenesis. Final technical report, August 1994--July 1997

The overall aims of the proposal were to identify intermediates in the process of methane formation from acetate. The specific aims were: (1) to characterize the mechanism of acetyl-CoA conversion to CH{sub 3}-H{sub 4}MPT, CO, and CoA and elucidate the mechanism of CO oxidation by the methanosarcina thermophila CO dehydrogenase/acetyl-CoA synthase (CODH/ACS), and (2) to study the mechanism of methyl-CoM reduction to methane by developing an activation protocol for methyl-CoM reductase (MCR) and identifying intermediates in the MCR mechanism. The authors also made significant progress toward accomplishing two other specific aims that were not included in the original proposal. These were: (1) to characterize the M. thermophila heterodisulfide reductase (HDR), and (2) to characterize the methyltetrahydromethanopterin: Coenzyme M methyltransferase from Methanosarcina mazei strain Goe1 in collaboration with Gerhard Gottschalk`s group. Results from these four studies are summarized

CprK crystal structures reveal mechanism for transcriptional control of halorespiration

Halorespiration is a bacterial respiratory process in which haloorganic compounds act as terminal electron acceptors. This process is controlled at transcriptional level by CprK, a member of the ubiquitous CRP-FNR family. Here we present the crystal structures of oxidized CprK in presence of the ligand ortho-chlorophenolacetic acid and of reduced CprK in absence of this ligand. These structures reveal that highly specific binding of chlorinated, rather than the corresponding non-chlorinated, phenolic compounds in the NH 2-terminal ß-barrels causes reorientation of these domains with respect to the central ¿-helix at the dimer interface. Unexpectedly, the COOH-terminal DNA-binding domains dimerize in the non-DNA binding state. We postulate the ligand-induced conformational change allows formation of interdomain contacts that disrupt the DNA domain dimer interface and leads to repositioning of the helix-turn-helix motifs. These structures provide a structural framework for further studies on transcriptional control by CRP-FNR homologs in general and of halorespiration regulation by CprK in particula