1,721,694 research outputs found
Analysis of genes involved in methanol oxidation in methylobacterium extorquens
No full textIn methylotrophic bacteria such as Methvlobacterium extorauens methanol is oxidised to Armaldehyde by methanol dehydrogenase (MDH) located in the periplasm. From MDH the electrons are passed along an electron transport chain including 2 cytochromes (cytochrome Cl and cytochrome ch) and finally to a terminal oxidase. The protons released from methanol oxidation form a proton motive force that can be utilised by ATP synthase to produce ATP for the energy requirements of the bacteria. Methanol dehydrogenase has a aiPz configuration. The X-ray structure of this enzyme showed that the active site is found in the a-subunit and contains the prosthetic group pyrrolo- quinoline quinone (PQQ). PQQ is sandwiched between the 'ceiling' of the active site formed by a unique disulphide bridge between adjacent cysteines (Cys 103, Cys 104) and the 'floor' of the active site formed by tryptophan 243. The active site of MDH also contains a calcium atom co-ordinated to both PQQ and 2 protein groups (Glu 177, Asn 261). The mechanism by which MDH catalyses the oxidation of methanol is poorly understood but an active site base (Asp 303) has been implicated in the reaction mechanism. There are at least 32 genes implicated in methanol oxidation. Most of these were identified in two species; Methvlobacterium extorquens and Paracoccus denitrificans. Although the functions of some of these genes have been determined many have not. This thesis describes work carried out to produce a site directed mutation in MDH changing aspartate 303 to a glutamate (D303E). Attempts to make mutations at other amino acids of MDH including active site residues (Arg331, Asn261, Glu 177 and Trp243) and a residue implicated in the interaction of MDH with cytochrome CL (Lys205) were unsuccessful probably due to the high GC content of the mxaP gene. To determine the roles of several methanol oxidation genes found in the large operon (mxaFJGIR(S)ACKLDB) in M.extorquens characterisation of mutants strains was undertaken. This indicated that expression of the a and P subunit genes (mxaF and mxal) is dependent upon each other. Mutations in mxaF. I, R, S and C resulted in strains that could not grow on methanol indicating that these genes have an essential role in methanol oxidation. Mutations in mxaD and in the intergenic region between mxaR and mxaS resulted in strains that could grow on methanol but the MDH activity was lower than wild-type MDH. A double mutant MDH which lacks calcium from the active site fmxaA") and contains an active site base mutation (D303E) was produced with the aim of reconstituting this enzyme with barium to produce an enzyme with potential for studying the reaction mechanism. This enzyme could not be reconstituted with calcium or barium probably because of the altered structure of the active site. Many of the site directed mutants of MDH have resulted in low levels of MDH expression and hence limiting characterisation. A study was carried out on the eSects of growth conditions on the expression of MDH from mutant strains of M.extorquens. This work indicated that changing pH, the concentration of tetracycline, the carbon substrates and the concentration of formaldehyde could not increase the expression of MDH from these mutant strains.</p
The role of modifiable work-related factors in retirement decisions. The health and employment after fifty, factors influencing retirement study (HEAF FIRST). A mixed methods study in the UK
No full textIncreased left expectancy coupled with decreased birth rates has resulted in an 'ageing society' with increases in the proportion of older people compared to traditional 'working age' people. Therefore, many countries are seeking to encourage working to older ages.This thesis explored the role that work-related factors play in individuals’ retirement decision-making, with a focus on factors that employers could potentially modify. Mixed-methods research was conducted in three phases.Phase one: Qualitative interviews were conducted with 17 recent retirees asking about factors which influenced their retirement. Thematic analysis showed that work-related factors were important, and both 'pushed' the retirees towards retirement, but also 'pulled' back towards work.Phase two: A systematic review was conducted to explore the evidence as to which work-related factors affected the decision to retire (since 2000). Over 150 factors had been investigated but the literature was heterogeneous. Overall, the most consistent evidence was for increased levels of job control and more appreciation at work being factors which reduced risk of retirement.Phase three: A nested case-control study was conducted within the Health and Employment After Fifty study. Questionnaires, informed by results from the two previous phases, were sent to incident retirees and age and sex-matched workers. After adjustment for age, sex, financial position, socio-economic position and marital status, the results showed that: job dissatisfaction; irregular hours; unhappiness with hours; effort reward imbalance; perception of declining standards; isolation at work; feelings of 'us vs them'; the demand-control-support model; being in a workplace that was not perceived to encourage later working; kneeling/squatting; commuting for more than 30 minutes; overnight stays; less flexibility; being constantly available; and work-life conflict were all factors associated with an increased risk of being retired.HEAF FIRST suggests that work-related factors are important in retirement decisions and the factors identified could be investigated in further studies and/or employer-led interventions
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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