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Search Results: 1 - 10 of 2992 matches for " Lisandro Horacio Otero "
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Different Effects of Mg2+ and Zn2+ on the Two Sites for Alkylammonium Compounds in Pseudomonas aeruginosa Phosphorylcholine Phosphatase
Lisandro Horacio Otero,Paola Rita Beassoni,Cristhian Boetsch,Angela Teresita Lisa,Carlos Eduardo Domenech
Enzyme Research , 2011, DOI: 10.4061/2011/918283
Abstract: Pseudomonas aeruginosa phosphorylcholine phosphatase (PchP) catalyzes the hydrolysis of phosphorylcholine (Pcho), is activated by Mg2+ or Zn2+, and is inhibited by high concentrations of substrate. This study has shown that PchP contains two sites for alkylammonium compounds (AACs): one in the catalytic site near the metal ion-phosphoester pocket, and the other in an inhibitory site responsible for the binding of the alkylammonium moiety. The catalytic mechanism for the entry of Pcho in both sites and Zn2+ or Mg2+ follows a random sequential mechanism. However, Zn2+ is more effective than Mg2+ at alleviating the inhibition produced by the entry of Pcho or different AACs in the inhibitory site. We postulate that Zn2+ induces a conformational change in the active center that is communicated to the inhibitory site, producing a compact or closed structure. In contrast, Mg2+ produces a relaxed or open conformation. 1. Introduction Pseudomonas aeruginosa phosphorylcholine phosphatase (PchP) catalyzes the hydrolysis of phosphorylcholine (Pcho) [1]. Pcho is the product of the action of hemolytic phospholipase C (PlcH) on phosphatidylcholine or sphingomyelin and is hydrolyzed to choline and inorganic phosphate (Pi) by the action of PchP. Thus, both the PlcH and PchP enzymes are involved in the pathogenesis of P. aeruginosa [2]. PchP contains three motifs that are characteristic of the enzymes belonging to the haloacid dehalogenase (HAD) superfamily [3]. Moreover, all three motifs have an important role in the catalytic process of Pcho or p-nitrophenylphosphate (p-NPP) in the presence of Mg2+, Zn2+, or Cu2+ as activators of the enzyme [4]. Using Pcho as the substrate, we have shown that Mg2+ is an equal activator for the enzyme at pH 5.0 and at pH 7.4; however, Zn2+ is an activator at pH 5.0 but an inhibitor at pH 7.4. The inhibition produced by Zn2+ at pH 7.4 is reversible and occurs in the presence or absence of Mg2+. This activation or inhibition of PchP by Zn2+ is caused by the transition from octahedral to tetrahedral geometry in the coordination sphere of the metal ion [5]. These results, in combination with the fact that PchP is inhibited by high Pcho concentrations and previous observations that different AACs may act as inhibitors of PchP [1, 6, 7], led us to evaluate the catalytic mechanism of PchP with Pcho as the substrate, Mg2+ or Zn2+ as activators, and AACs as inhibitors. 2. Materials and Methods 2.1. Materials Isopropyl-β-D-thiogalactopyranoside (IPTG) and HisLinkTM resin were purchased from Promega. Pcho and p-NPP were purchased from
Phosphorylcholine Phosphatase: A Peculiar Enzyme of Pseudomonas aeruginosa
Carlos Eduardo Domenech,Lisandro Horacio Otero,Paola Rita Beassoni,Angela Teresita Lisa
Enzyme Research , 2011, DOI: 10.4061/2011/561841
Abstract: Pseudomonas aeruginosa synthesizes phosphorylcholine phosphatase (PchP) when grown on choline, betaine, dimethylglycine or carnitine. In the presence of Mg2+ or Zn2+, PchP catalyzes the hydrolysis of p-nitrophenylphosphate (p-NPP) or phosphorylcholine (Pcho). The regulation of pchP gene expression is under the control of GbdR and NtrC; dimethylglycine is likely the metabolite directly involved in the induction of PchP. Therefore, the regulation of choline metabolism and consequently PchP synthesis may reflect an adaptive response of P. aeruginosa to environmental conditions. Bioinformatic and biochemistry studies shown that PchP contains two sites for alkylammonium compounds (AACs): one in the catalytic site near the metal ion-phosphoester pocket, and another in an inhibitory site responsible for the binding of the alkylammonium moiety. Both sites could be close to each other and interact through the residues 42E, 43E and 82YYY84. Zn2+ is better activator than Mg2+ at pH 5.0 and it is more effective at alleviating the inhibition produced by the entry of Pcho or different AACs in the inhibitory site. We postulate that Zn2+ induces at pH 5.0 a conformational change in the active center that is communicated to the inhibitory site, producing a compact or closed structure. However, at pH 7.4, this effect is not observed because to the hydrolysis of the [Zn2+L2 ?1L2 0(H2O)2] complex, which causes a change from octahedral to tetrahedral in the metal coordination geometry. This enzyme is also present in P. fluorescens, P. putida, P. syringae, and other organisms. We have recently crystallized PchP and solved its structure. 1. Introduction Bacteria possess multiple proteins with the capacity to catalyze the hydrolysis of phosphoric esters in either acidic or alkaline media. In addition to having different optimal pH values for their activity, these enzymes differ in their dependence on metal ions, which are generally divalent cations found in the second or third period of the periodic table. In our previous review, we summarized work showing that the synthesis of Pseudomonas aeruginosa phosphorylcholine phosphatase (PchP) in the presence of low or high orthophosphate concentration depends on choline, betaine, dimethylglycine, or carnitine added to the culture medium as the carbon and/or nitrogen source. In addition, the gene for PchP was located, and the most current information on the kinetic, biochemical, biophysical, and molecular characteristics of PchP was summarized [1]. Phosphorylcholine (Pcho), phosphorylethanolamine, and p-nitrophenylphosphate (p-NPP),
ESTRATEGIAS DE DECISIóN EN SISTEMAS DINáMICOS: APLICANDO MAPAS COGNITIVOS DIFUSOS APLICACIóN A UN EJEMPLO SOCIO – ECONóMICO
Leopoldo Lisandro Horacio Curia,Andrea Lina Lavalle
JISTEM - Journal of Information Systems and Technology Management , 2011,
Abstract: Situations in which human beings develop their daily tasks are extremely complex and dynamic.In each field, the analysis of the system`s variables under consideration can be simplified if thesystem is conceived as a set of concepts, where a change in each of them will cause changes inthe remainder. In the analysis of a particular problem, the representation of concepts in the formof a map helps to synthesize information detecting the main concepts that are linked to theproblem. In these cases, Fuzzy Cognitive Maps (FCM) are able to synthesize much of thisinformation. Also with this technique is possible to follow the evolution of the concepts to a stateof equilibrium and therefore allow us to study the dynamics that takes the passage from one stateto another given the situation under review. This paper describes the construction and analysis ofthe Fuzzy Cognitive Maps technique through an economy application example. The aim is topresent a methodology supported by the FCM to analyze the evolution and impact on the systemcausing by the change in the value of one or more concepts involved.
Las creencias involuntarias en Sexto Empírico y Hume
Aguirre,Lisandro;
T?3picos , 2008,
Abstract: the object of study in this paper is belief. our aim is to show how, through this concept, hume's modern and pirro's ancient scepticism may converge into a fairly similar position. both the theoretical and at the same time practical attitudes consider it licit to "assent to what presents itself to man in an unavoidable way and independently from our will". as we now, there is for sixtus as well as for hume something, regardless of the name we give it ("phainómenon", "perceptions"), which "induces" us to or "demands" assent from us, [the latter being] a fundamental term which seems to indicate a concept common to both, ancient scepticism and hume's thought. would it then be legitimate or justified to keep giving our support to that statement of history that called hume first an "empiricist" and afterwards a "naturalist"? would it not be more accurate to trace some pirronism, even unconscious, in the scot's ideas? our answer starts off from michael frede's non-traditional interpretation, who somewhat firmly set up the idea that the sceptical resign having beliefs, or at least, can have them without by it trespassing the epoché. the central issue will then be to determine which meaning should be attributed to the term "belief".
De la era de la revolución al imperio de la identidad: interpretando la modernidad en América Latina
Gallucci, Lisandro;
Perfiles latinoamericanos , 2009,
Abstract: the issue of modernity has held a central place in latin america's history and, for that reason, it has been the object of numerous reflections from a wide variety of disciplines and theoretical perspectives. however, most of these reflections have maintained a canonical definition of modernity, which conceives it as a linear and accumulative rationalization process. this vision has had important implications for latin american societies. thus, a critical revision of the very idea of modernity and the ways in which it has been perceived in latin america could result in new keys for interpreting the historical trajectories of our societies.
La vida política de los instrumentos: Imágenes y prácticas de los sectores subalternos en el Neuquén de la primera mitad del siglo XX
Gallucci,Lisandro;
Quinto sol , 2008,
Abstract: this article deals with the forms of political action of subaltern people in a particular space of peripheral argentina: neuquenian municipalities of the first half of the 20th century. even when national territories were excluded from the federal political system, the recreation in these spaces of some of the so called creole politics provides an opportunity to explore the complexity of political clientelism in those decades of argentinian history. furthermore, this paper pays attention to interactions between local elites and the inferior members of the clientships, observing the ways in which the latter were represented, thus shaping the relationships that both sectors kept between them. albeit subaltern sectors of territorian neuquen did not consolidate themselves as an autonomous political actor, it is interesting to call attention over the negotiations they were capable to maintain with local political elites. it is suggested in this paper that clientelistic practices, as the explanations constructed on them did so, contributed to shape some of the features of the argentinian political culture of that time.
Las prácticas electorales en un municipio patagónico: Neuquén, 1904-1916
Gallucci,Lisandro;
Revista Pilquen , 2005,
Abstract: this article offers an approach to the electoral practices developed in the city of neuquén during its first years of political life. our main interest is put on the analysis of those practices as a dimension of political citizenship in an outlying space of argentina as the territorian neuquen was. besides the rules that regulated communal elections in national territories, the ways in which local population experienced them are also studied. along those lines, it is of our interest to inquire about the different modes of participation existing in the municipality. this article looks to recover the importance of territorian political history, traditionally relegated into a marginal place in patagonian historiography.
Las creencias involuntarias en Sexto Empírico y Hume
Lisandro Aguirre
T?3picos , 2008,
Abstract: El objeto de estudio de este trabajo es la creencia. Nuestro objetivo es mostrar cómo a través de ese concepto el escepticismo moderno de Hume y el antiguo de Pirrón pueden llegar a converger en una posición bastante similar. Ambas actitudes teóricas y a la vez prácticas consideran que es lícito dar "asentimiento a aquello que se presenta al hombre de modo inevitable e independientemente de nuestra voluntad. Sabemos que tanto para Sexto como para Hume hay algo, independientemente del nombre que le demos ("phainómenon", "perceptions"), que nos "induce" o nos "exige" asentimiento, término fundamental que parece indicar un concepto común al escepticismo antiguo y al pensamiento de Hume. Será entonces legítimo o justificado seguir apoyando el juicio de la historia que calificó en un principio a Hume de "empirista" o posteriormente de "naturalista"? No será más exacto rastrear cierto pirronismo, aunque sea inconsciente, en las ideas del escocés? Nuestra respuesta parte de la interpretación no tradicional de Michael Frede que fundamentó con cierta solidez la idea de que el escéptico no renuncia a tener creencias o, al menos, puede tenerlas sin infringir con ello la epoché. La cuestión central será entonces determinar qué significado habría que atribuir al término "creencia". The object of study in this paper is belief. Our aim is to show how, through this concept, Hume's modern and Pirro's ancient scepticism may converge into a fairly similar position. Both the theoretical and at the same time practical attitudes consider it licit to "assent to what presents itself to man in an unavoidable way and independently from our will". As we now, there is for Sixtus as well as for Hume something, regardless of the name we give it ("phainómenon", "perceptions"), which "induces" us to or "demands" assent from us, [the latter being] a fundamental term which seems to indicate a concept common to both, ancient scepticism and Hume's thought. Would it then be legitimate or justified to keep giving our support to that statement of history that called Hume first an "empiricist" and afterwards a "naturalist"? Would it not be more accurate to trace some pirronism, even unconscious, in the Scot's ideas? Our answer starts off from Michael Frede's non-traditional interpretation, who somewhat firmly set up the idea that the sceptical resign having beliefs, or at least, can have them without by it trespassing the epoché. The central issue will then be to determine which meaning should be attributed to the term "belief".
La paz del trigo: Cultura legal y sociedad local en el desarrollo agropecuario pampeano, 1890-1945
Lisandro Gallucci
Prohistoria , 2006,
Abstract:
Cinema, televis o e autoria: a fic o seriada e os filmes do melodrama
Nogueira, Lisandro
Sess?es do Imaginário , 2003,
Abstract: Enquanto as telenovelas latino-americanas de língua espanhola e as soopoperas prescindem da figura do "autor", as brasileiras absorveram o termo a partir do contexto vanguardista dos anos 60 que originou o cinema de autor. A tens o entre criar e seguir normas da televis o, revelou que os limites para o escritor dependem do contexto histórico, das oscila es da audiência e da dinamica da indústria cultural.
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