923 resultados para Redox mediation


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Mode of access: Internet.

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Published in conjunction with a symposium held in Washington, D.C., 1997.

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Mode of access: Internet.

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A finite difference method for simulating voltammograms of electrochemically driven enzyme catalysis is presented. The method enables any enzyme mechanism to be simulated. The finite difference equations can be represented as a matrix equation containing a nonlinear sparse matrix. This equation has been solved using the software package Mathematica. Our focus is on the use of cyclic voltammetry since this is the most commonly employed electrochemical method used to elucidate mechanisms. The use of cyclic voltammetry to obtain data from systems obeying Michaelis-Menten kinetics is discussed, and we then verify our observations on the Michaelis-Menten system using the finite difference simulation. Finally, we demonstrate how the method can be used to obtain mechanistic information on a real redox enzyme system, the complex bacterial molybdoenzyme xanthine dehydrogenase.

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Cytochrome c biogenesis in Escherichia coli is a complex process requiring at least eight genes (ccmABC DEFGH). One of these genes, ccmG, encodes a thioredoxin-like protein with unusually specific redox activity. Here, we investigate the basis for CcmG function and demonstrate the importance of acidic residues surrounding the redox-active center.

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Apropos the basal ganglia, the dominant striatum and globus pallidus internus (GPi) have been hypothesised to represent integral components of subcortical language circuitry. Working subcortical language theories, however, have failed thus far to consider a role for the STN in the mediation of linguistic processes, a structure recently defined as the driving force of basal ganglia output. The aim of this research was to investigate the impact of surgically induced functional inhibition of the STN upon linguistic abilities, within the context of established models of basal ganglia participation in language. Two males with surgically induced 'lesions' of the dominant and non-dominant dorsolateral STN, aimed at relieving Parkinsonian motor symptoms, served as experimental subjects. General and high-level language profiles were compiled for each subject up to 1 month prior to and 3 months following neurosurgery, within the drug-on state (i.e., when optimally medicated). Comparable post-operative alterations in linguistic performance were observed subsequent to surgically induced functional inhibition of the left and right STN. More specifically, higher proportions of reliable decline as opposed to improvement in post-operative performance were demonstrated by both subjects on complex language tasks, hypothesised to entail the interplay of cognitive-linguistic processes. The outcomes of the current research challenge unilateralised models of functional basal ganglia organisation with the proposal of a potential interhemispheric regulatory function for the STN in the mediation of high-level linguistic processes.

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Cyclosporine A-treated transplant recipients develop pronounced cardiovascular disease and have increased oxidative stress and altered antioxidant capacity in erythrocytes and plasma. These experiments investigated the time-course of cyclosporine A-induced changes to redox balance in plasma and erythrocytes. Rats were randomly assigned to either a control or cyclosporine A-treated group. Treatment animals received 25 mg/kg of cyclosporine A via intraperitoneal injection for either 7 days or a single dose. Control rats were injected with the same volume of the vehicle. Three hours after the final injections, plasma was analysed for total antioxidant status, a-tocopherol, malondialdehyde, and creatinine. Erythrocytes were analysed for reduced glutathione (GSH), alpha-tocopherol, methaemoglobin, malondialdehyde, and the activities of superoxide dismutase, catalase, GSH peroxidase, and glucose-6-phosphate dehydrogenase (G6PD). Cyclosporine A administration for 7 days resulted in a significant increase (P < 0.05) in plasma malondialdehyde, methaemoglobin, and superoxide dismutase and catalase activities. There was a significant decrease (P < 0.05) in erythrocyte GSH concentration and G6PD activity in cyclosporine A animals. There were no significant differences (P > 0.05) between groups following a single dose of cyclosporine A in any of the measures. In summary, cyclosporine A alters erythrocyte redox balance after 7 days administration, but not after a single dose.

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A MerR-like regulator (NmlR -Neisseria merR-like Regulator) identified in the Neisseria gonorrhoeae genome lacks the conserved cysteines known to bind metal ions in characterized proteins of this family. Phylogenetic analysis indicates that NmlR defines a subfamily of MerR-like transcription factors with a distinctive pattern of conserved cysteines within their primary structure. NmlR regulates itself and three other genes in N. gonorrhoeae encoding a glutathione-dependent dehydrogenase (AdhC), a CPx-type ATPase (CopA) and a thioredoxin reductase (TrxB). An nmlR mutant lacked the ability to survive oxidative stress induced by diamide and cumene hydroperoxide. It also had > 50-fold lower NADH-S-nitrosoglutathione oxidoreductase activity consistent with a role for AdhC in protection against nitric oxide stress. The upstream sequences of the NmlR regulated genes contained typical MerR-like operator/promoter arrangements consisting of a dyad symmetry located between the -35 and -10 elements of the target genes. The NmlR target operator/promoters were cloned into a beta-galactosidase reporter system and promoter activity was repressed by the introduction of NmlR in trans. Promoter activity was activated by NmlR in the presence of diamide. Under metal depleted conditions NmlR did not repress P-AdhC (or P-CopA) promoter activity, but this was reversed in the presence of Zn(II), indicating repression was Zn(II)-dependent. Analysis of mutated promoters lacking the dyad symmetry revealed constitutive promoter activity which was independent of NmlR. Gel shift assays further confirmed that NmlR bound to the target promoters possessing the dyad symmetry. Site-directed mutagenesis of the four NmlR cysteine residues revealed that they were essential for activation of gene expression by NmlR.