Copper binding of the glycolytic enzyme glyceraldehyde 3-phosphate dehydrogenase in Staphylococcus aureus

PhD ThesisStaphylococcus aureus is a Gram positive bacterium which is predominantly commensal, but which can also be a human and animal pathogen, able to cause serious infections. It is becoming an increasing problem due to it becoming resistant to modern antibiotics. In common with most bacteria, S. aureus requires small quantities of the essential metal copper, but they also experience toxicity when exposed to high concentrations of copper, a metal that has been used for its antimicrobial properties for centuries. However, the mechanism of such toxicity remains elusive. Here, the effect of copper toxicity on S. aureus has been investigated in order to understand how excess copper ions affect its physiology. The growth of S. aureus was found to be inhibited in media containing elevated copper, and the extent of this inhibition was shown to be dependent on the type of growth medium used. Analysis of soluble extracts from S. aureus cells exposed to elevated copper led to the identification of a cytoplasmic enzyme, GapA, which binds copper. GapA is a member of the wellcharacterised family of the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) enzymes, and is not a metalloprotein. Copper inhibition of the activity of the S. aureus GapA enzyme was demonstrated, both in S. aureus cell extracts and with recombinant enzyme in vitro, using a specific enzyme activity assay. Analysis of the purified recombinant GapA enzyme in vitro demonstrated a copper binding stoichiometry of one Cu(I) ion to each GapA monomer using analytical sizeexclusion chromatography and spectrophotometry, and evidence is presented that suggests high affinity Cu(I) binding of biochemical relevance. Some preliminary evidence is provided that the Cu(I) binding site on the GapA protein includes the thiol group of cysteine 151 located within the active site, consistent with predictions based on published crystal structures, and explaining the observed copper-dependent inhibition of enzyme activity. This is the first evidence of copper binding to a non-metalloprotein within the cytoplasm of S. aureus and adds to mounting evidence that aberrant binding of copper to cytosolic proteins contributes to bacterial copper toxicity

A Survey of Malaria in the British Army in West Africa

Abstract Not Provided

Fixation Condition Effects on Stop Signal Reaction Times: An Eye-Hand Co-ordinated Human Countermanding Task

The countermanding task requires subjects to cancel an impending movement in the presence of an imperative stop signal. The outcome of a given countermanding trial has been modeled as a race between stochastically independent GO and STOP processes and is largely dependent on the amount of time between target and stop signal presentation (the stop signal delay - SSD). Here, we investigated the effect of fixation condition on the GO and STOP processes using human subjects in eye-only, hand-only and eye-hand co-ordinated countermanding tasks. In Experiment 1, we found that duration of the STOP process, estimated through the derivation of the stop signal reaction time (SSRT), was ~20 ms shorter on trials with a 200 ms gap between fixation point removal and target presentation compared to when the fixation point remained illuminated (an “overlap” condition). Similarly, we found SSRTs were ~10 ms shorter on trials with simultaneous fixation point removal and target presentation compared to the overlap condition. However, in Experiment 2, this priming of movement inhibition due to fixation condition disappeared, when the stop signal delay for each trial was determined dynamically, based on subject performance on previous trials. Overall, we suggest the disappearance of fixation condition effects in Experiment 2 was due to smaller gap effects on reaction times and a greater variance in fixation condition effects on the STOP process in Experiment 2. We believe these differences arose due to a higher percentage of trials in Experiment 2 where the GO and STOP processes approached threshold at approximately the same time. Therefore we postulate that such trials produce a greater amount of conflict between movement generation and inhibition systems, causing both systems to rely less on fixation cues

Is the Connection Effective? Through the Maze of Section 864

This article discusses certain of the rules under which foreign corporations and nonresident alien individuals may be subjected to United States federal income tax. It may at first be surprising that there are any situations in which the United States would attempt to tax the income of a nonresident alien or a foreign corporation. A moment\u27s reflection, however, will reveal that in some situations it is quite logical that the United States should tax at least a portion of the income of such persons. For example, it seems reasonable that a corporation which conducts some minimum level of business in the United States should be subjected to United States tax on the income from the business regardless of whether the corporation is incorporated domestically or abroad. Similarly, if an alien individual, though not resident in the United States, conducts business here through agents or employees, should not the income of that business be subjected to United States tax

Is the Connection Effective? Through the Maze of Section 864

This article discusses certain of the rules under which foreign corporations and nonresident alien individuals may be subjected to United States federal income tax. It may at first be surprising that there are any situations in which the United States would attempt to tax the income of a nonresident alien or a foreign corporation. A moment\u27s reflection, however, will reveal that in some situations it is quite logical that the United States should tax at least a portion of the income of such persons. For example, it seems reasonable that a corporation which conducts some minimum level of business in the United States should be subjected to United States tax on the income from the business regardless of whether the corporation is incorporated domestically or abroad. Similarly, if an alien individual, though not resident in the United States, conducts business here through agents or employees, should not the income of that business be subjected to United States tax

Marine exploration

Less than 50 years ago knowledge of the geology of the UK continental shelf (UKCS) was extremely limited. The BGS marine geoscience programme began about 40 years ago in response to the development of the UK oil and gas industry. The BGS was funded by the then Department of Energy to carry out a national mapping programme based on geophysical data, seabed samples and boreholes. By the 1990s, geological maps at a scale of 1:250 000 were published for the shelf regions showing seabed sediments, Quaternary geology and bedrock. The deeper water areas to the north and west continue to be explored with support from the oil industry. A series of regional reports, the offshore equivalent of the BGS regional guides, were published and reports for the Atlantic Margin will be published in 2010. MAREMAP is a new multidisciplinary environmental mapping programme designed to underpin the new marine industries and environmental issues