The reduction of acetylpyridine adenine dinucleotide by NADH: is it a significant reaction of proton-translocating transhydrogenase, or an artefact?

AbstractTranshydrogenase is a proton pump. It has separate binding sites for NAD+/NADH (on domain I of the protein) and for NADP+/NADPH (on domain III). Purified, detergent-dispersed transhydrogenase from Escherichia coli catalyses the reduction of the NAD+ analogue, acetylpyridine adenine dinucleotide (AcPdAD+), by NADH at a slow rate in the absence of added NADP+ or NADPH. Although it is slow, this reaction is surprizing, since transhydrogenase is generally thought to catalyse hydride transfer between NAD(H) – or its analogues and NADP(H) – or its analogues, by a ternary complex mechanism. It is shown that hydride transfer occurs between the 4A position on the nicotinamide ring of NADH and the 4A position of AcPdAD+. On the basis of the known stereospecificity of the enzyme, this eliminates the possibilities of transhydrogenation (a) from NADH in domain I to AcPdAD+ wrongly located in domain III; and (b) from NADH wrongly located in domain III to AcPdAD+ in domain I. In the presence of low concentrations of added NADP+ or NADPH, detergent-dispersed E. coli transhydrogenase catalyses the very rapid reduction of AcPdAD+ by NADH. This reaction is cyclic; it takes place via the alternate oxidation of NADPH by AcPdAD+ and the reduction of NADP+ by NADH, while the NADPH and NADP+ remain tightly bound to the enzyme. In the present work, it is shown that the rate of the cyclic reaction and the rate of reduction of AcPdAD+ by NADH in the absence of added NADP+/NADPH, have similar dependences on pH and on MgSO4 concentration and that they have a similar kinetic character. It is therefore suggested that the reduction of AcPdAD+ by NADH is actually a cyclic reaction operating, either with tightly bound NADP+/NADPH on a small fraction (<5%) of the enzyme, or with NAD+/NADH (or AcPdAD+/AcPdADH) unnaturally occluded within the domain III site. Transhydrogenase associated with membrane vesicles (chromatophores) of Rhodospirillum rubrum also catalyses the reduction of AcPdAD+ by NADH in the absence of added NADP+/NADPH. When the chromatophores were stripped of transhydrogenase domain I, that reaction was lost in parallel with `normal reverse' transhydrogenation (e.g., the reduction of AcPdAD+ by NADPH). The two reactions were fully recovered upon reconstitution with recombinant domain I protein. However, after repeated washing of the domain I-depleted chromatophores, reverse transhydrogenation activity (when assayed in the presence of domain I) was retained, whereas the reduction of AcPdAD+ by NADH declined in activity. Addition of low concentrations of NADP+ or NADPH always supported the same high rate of the NADH→AcPdAD+ reaction independently of how often the membranes were washed. It is concluded that, as with the purified E. coli enzyme, the reduction of AcPdAD+ by NADH in chromatophores is a cyclic reaction involving nucleotides that are tightly bound in the domain III site of transhydrogenase. However, in the case of R. rubrum membranes it can be shown with some certainty that the bound nucleotides are NADP+ or NADPH. The data are thus adequately explained without recourse to suggestions of multiple nucleotide-binding sites on transhydrogenase

Proton translocating nicotinamide nucleotide transhydrogenase from E. coli. Mechanism of action deduced from its structural and catalytic properties11This review is dedicated to the memory of Professor Lars Ernster.

AbstractTranshydrogenase couples the stereospecific and reversible transfer of hydride equivalents from NADH to NADP+ to the translocation of proton across the inner membrane in mitochondria and the cytoplasmic membrane in bacteria. Like all transhydrogenases, the Escherichia coli enzyme is composed of three domains. Domains I and III protrude from the membrane and contain the binding site for NAD(H) and NADP(H), respectively. Domain II spans the membrane and constitutes at least partly the proton translocating pathway. Three-dimensional models of the hydrophilic domains I and III deduced from crystallographic and NMR data and a new topology of domain II are presented. The new information obtained from the structures and the numerous mutation studies strengthen the proposition of a binding change mechanism, as a way to couple the reduction of NADP+ by NADH to proton translocation and occurring mainly at the level of the NADP(H) binding site

Controle de l'activite de l'ATP synthase des chloroplastiques par lesprotons et implications mecanistiques

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : TD 81143 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

L’éco-épidémiologie

Afin de résoudre les problèmes de santé publique posés par l’épidémiologie des facteurs de risque centrée sur l’individu, et négligeant les processus causals en œuvre reliant les facteurs d’exposition aux maladies, Mervyn Susser a proposé une épidémiologie multiniveau appelée éco-épidémiologie. Celle-ci rend compte de l’interdépendance des individus et de la connexion entre différents niveaux d’organisation (moléculaires, individuels, socio-environnementaux) participant au processus causal des maladies. Le but de cette épidémiologie est d’intégrer plus d’un niveau d’organisation dans la conception, l’analyse et l’interprétation des problèmes de santé. Après avoir formulé les principales critiques de l’épidémiologie des facteurs de risque centrée sur le seul niveau individuel, nous nous attacherons à montrer comment l’éco-épidémiologie et ses développements pourraient permettre de comprendre la nécessité d’une conception plus large de l’épidémiologie, associant les études qui visent à identifier les facteurs de risque et celles qui cherchent à répondre à d’autres questions tout aussi importantes pour la santé publique

L’histoire familiale dans les écrits d’assistance éducative

How family history is referred to in « educational assistance » writings                 The French procedure of « educational assistance » requires the juvenile court to order educative measures as soon as it is assumed that the child is in danger within his own family. According to the French civil law, the notion of danger is the very condition of the action of the magistrate in such a matter but there is no precise definition of danger; the law only mentions that the action of the judge is well-founded if « the health, the security, the morality and the conditions of education of the child are seriously endangered ». In such a context, how is family history referred to by social workers, in order to back up the notion of danger ?To answer to that question, the court records of a family known over 3 generations have been examined. The analysis of the first writings (« signalements ») mentioning an actual danger and requiring “educational assistance” shows that references are systematically made to the the child’s siblings’ institutional history, rather than to the previous generations’. On the other hand, very few of the family history itself is mentioned.We can also observe a subtle evolution in the writings made in the course of the assistance. First, the social workers and the family are expecting from each other to acknowledge their own model of education, both sides confronting their representations of parenthood. Then comes the time when both parents and social workers bring themselves to accept the others with their own specific representations of how to act like parents. At the same time there is a second process at work. References to previous events or behaviours are progressively rubbed out from the children’s record, as they become parents themselves; then the source of danger is removed from the adults’ side to the children’s. Thus, in the concern about having an objective analysis of the present situation, the social worker eliminates all historical arguments from his reasoning, just as if he now regarded these previously alleged elements of danger as irrelevant

Décision médicale et rationalité (l'incertitude d'une action)

Acte consistant à faire un choix éclairé entre différentes possibilités, la décision médicale est le résultat d un jugement que le médecin porte sur cette situation concrète et incertaine constituée par la rencontre avec le patient, et ne peut se ramener à une procédure formelle reliant diagnostic et prescription. Ce travail s attachera, dans ce contexte d action, à repérer les contraintes liées à la décision: le patient, être intime et être social, le médecin, pris dans un savoir représenté par les données acquises de la science et un savoir-faire destinés à concilier l universel et le particulier, la société, exigeant efficacité et justification de nos actes. Ensuite, la notion d incertitude sera abordée, par l intermédiaire d une analyse critique des essais cliniques, en décrivant leur construction, la possibilité de leur synthèse, afin de savoir ce que signifiera, pour la pratique médicale, leur utilisation systématique comme instrument de preuve. Enfin, la question de la rationalité de la décision médicale sera posée, en confrontant une rationalité instrumentale caractérisée par l emploi des meilleurs moyens pour atteindre une fin définie, et une rationalité procédurale, que l Evidence-Based Medicine semble adopter en partie. Une autre rationalité devra être construite, en mettant en perspective les faits d expérimentation dans le domaine pratique, supposant qu un passage est possible entre ce que la méthode scientifique a permis, dans un contexte d explication d un monde théorique construit, et ce que l expérience a rendu visible, dans un contexte de compréhension de ce qu attend de nous le patientMedical decision, as an act consisting of doing a choice among different alternatives, results from a judgment done by a medical doctor in face of a patient and cannot be reduced to a formal procedure between diagnosis and prescription. The aim of this study was first to analyse the different constraints linked to the medical decision-making: the patient, viewed as an intimate and social being, the medical doctor, trying to accord his knowledge with his know-how with intent to conciliate the particular with the universal, the society, which requires efficacy and justification of our acts. The notion of uncertainty was then explored through a critical analysis of the clinical trials with emphasis on construction and possibility of synthesis in order to know what could signify their systematic use as an instrument of evidence in a practical point of view. Finally, the medical rationality was questioned, by confronting the instrumental rationality characterized by the use of the best means for reaching a defined end, and a procedural rationality adopted in part by the Evidence-Based Medicine. Another rationality need to be constructed, where experimental data must be interpreted again practically. In this perspective, a passage must be supposed between theory as an explication of a constructed world and practice as a comprehension of what the patient expects from usPARIS-EST Marne-la-Vallee-BU (774682101) / SudocSudocFranceF

A first step toward assessing organizational identification in a university setting

Organizational culture research has been steadily growing during the last two decades, and has become an essential component for assessing an organization\u27s capacity to adapt and survive. Discovering the underlying assumptions within an organization offers a more accurate insight on how its members perceive, think, and feel about the environment they work in, thus providing the opportunity of assessing the group\u27s cohesiveness and culture strength. This study was designed to establish an initial assessment of an organization within a university setting, and to provide insight to its membership sense of identification. The study reflects the analysis of different information made available through visible artifacts, as well as perceptions from its members via a self-identification questionnaire

Mesure de la qualité de vie et de la santé perceptuelle chez des sujets âgés à distance d'une réanimation prolongée après chirurgie cardiaque

Les progrès médicaux, associés à l'augmentation de l'espérance de vie, conduisent à proposer une chirurgie cardiaque à des patients de plus en plus âgés et fragiles. Le bénéfice de tels gestes s'évalue donc plutôt en terme de qualité de vie qu'en augmentation de sa durée. Méthode: Le devenir des patients âgés de plus de 65 ans, dont l'évolution initiale avait été marquée par une réanimation prolongée, a été évalué à travers le questionnaire SF-36, par rapport à un échantillon contrôle apparié. Discussion : la morbi-mortalité induite, non négligeable, est pondérée par la relative qualité de vie à 18 mois de ces patients vis à vis d'une population de référence, malgré quelques limitations, et hors considérations économiques.NANTES-BU Médecine pharmacie (441092101) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF