/library/oar/handle/123456789/33291 2025-12-29T12:33:45Z 2025-12-29T12:33:45Z /library/oar/handle/123456789/77757 2024-02-09T11:09:11Z 1996-01-01T00:00:00Z

Title: Cloning of Escherichia Coli iron superoxide dismutase in yeast cells deficient in copper, zinc superoxide dismutase Abstract: An episomal and a centromeric plasmid were used in the cloning of ‘Esherichia coli’ iron superoxide dismutase (FeSOD) in ‘Saccharomyces cervisiae’ cells deficient in copper, zinc superoxide dismutase (Cu,ZnSOD). In both cases the ‘E.coli’ FeSOD gene was unde the transcriptional control of the yeast PGK promoter. The prokaryotic FeSOD was shown to be functionally expressed at different levels within the two recombinant strains. Moreover, the FeSOD activity was found to decrease as the cells approached stationary phase in both strains. This decrease is attributed to the decrease in glucose concentration within the fixed volume medium. Description: M.PHIL.

1996-01-01T00:00:00Z /library/oar/handle/123456789/77748 2021-06-28T08:23:09Z 1996-01-01T00:00:00Z

Title: Isolation and characterization of a superoxide dismutase from the mollusc Helix Aspera Abstract: It is well established that antioxidant defences have a crucial role to play in living organisms, especially during periods of over production of reactive oxygen species such as superoxides. In the first line of the defence is the enzyme superoxide dismutase (EC 1.15 .1.1) which catalyses the disputation of superoxide radicals and is, as a result, widely distributed throughout the plant and animal kingdoms. In view of the interest of superoxide dismutases not only from an evolutionary standpoint but also because of their potential in the management of free-radical diseases and as part of our studies on the structure - function relationships of these enzymes we have purified and characterised a copper/zinc superoxide dismutase Cu/ZnSOD from the pulmonate mollusc, Helix aspersa. Description: M.PHIL.

1996-01-01T00:00:00Z /library/oar/handle/123456789/77241 2021-10-15T15:12:27Z 1975-01-01T00:00:00Z

Title: Haemoglobin abnormalities in the Maltese Abstract: The mean of haemoglobin concentration in 335 cord blood samples was 16.0 g/dl 2.6 S.D. The haemoglobin concentration was lower from the mean by more than 2 S.D. (10.8g/dl) in 10 (2.9%) neonates. Extra-corpuscular factors are the main cause of anaemia in the newborn. a-Thalessaemia is absent or extremely rare in the Maltese. Haemoglobin F Malta I was was detected in 1.6 percent of 2600 cord bloods screened by starch gel electrophoresis. One child had the double heterozygozity for haemoglobin F Malta I and 8-thalassaemia. So long as Haemoglobin F Malta I is not detected in these cases, the G locus must be assumed to be suppressed in 8-thalassaemia. Description: M.PHIL.

1975-01-01T00:00:00Z /library/oar/handle/123456789/33318 2020-11-09T09:24:36Z 1995-01-01T00:00:00Z

Title: Oxidative stress and expression of superoxide dismutase in escherichia coli and thermus aquaticus Abstract: Escherichia coli is a facultative anaerobe and mesophile which produces two types of superoxide dismutase, iron (FeSOD) and manganese (MnSOD), the latter under the control of several global regulators of gene expression. Although much is known about the control ofMnSOD expression, FeSOD has always been assumed to be constitutively expressed. However, it has been suggested that the Fur (ferric uptake regulation) protein may be an inducer of this gene. Conflicting reports in the literature about the oxidative stress response of E.coli which overproduce plasmid-encoded FeSOD where addressed by assessing the types of plasmid used and, in particular, the type of promoter encoded by the plasmid. Strains which overproduced FeSOD unqer the control of the natural (wild-type) promoter were more sensitive to paraquat-induced oxidative stress than were wild type E. coli. Strains which overproduced F eSOD under the control of the artificial trc promoter were less sensitive to oxidative stress. Therefore the FeSOD promoter has a significant influence on the physiological response of the cell to oxidative stress and this result may be suggestive of a further mechanism of regulation. The gene encoding MnSOD from E. coli was cloned and expressed in several different E. coli strains. Tt was found that a manganese supplemented medium was required for the full activity of the enzyme, a result which explains other findings in the literature. In direct contrast, Thermus aquaticus is an obligate aerobe and thermophile which produces only MnSOD and although its gene has been cloned, nothing is known about the response of this important enzyme to oxidative stress in this organism. A bench-top 5 litre fermenter was installed as part of this work and facilitated experiments to investigate oxidative stress in Thermus aquaticus whereby pH and dissolved oxygen levels could be accurately monitored and controlled. A twofold increase in the expression and corresponding activity ofMnSOD was observed when Thermus aquaticus was subjected to oxidative stress using 200 µM paraquat. Surprisingly, no effect was observed when culture conditions included pure oxygen supplied at ambient pressure. A reduction in MnSOD activity was observed when using minimal broth which lacked manganese supplementation, an effect repeated when the iron concentration in the medium was increased. This is suggestive of an in vivo metal substitution in the MnSOD enzyme similar to that described for E. coli MnSOD. The fermentation technology employed to study T. aquaticus was used to investigate conditions for maximum expression and yield of recombinant human MnSOD which may in the near future gain pharmacological relevance. E. coli were used to express this protein under the control of the trc promoter and both maximal expression and cell yield were obtained using a glycerol and phosphate rich broth (terrific broth) Co-overexpression of the E. coli chaperonins GroES and GroEL from a second plasmid resulted in a slight (1.8 fold) increase in the measured specific activity of the SOD enzyme. This contrasts with the 3 fold increase previously observed with human copper-zinc SOD in the presence of these protein chaperones and may reflect a non-specific selectivity of these chaperones for β-sheet proteins (i.e. Copper-zinc SOD) over predominantly a-helical ones (i.e. MnSOD). During investigations on E. coli SOD expressiOn, a previously unreported band of SOD-like activity was observed only AFTER incubation of native polyacrylamide gels with hydrogen peroxide at 5 mM. Further investigation ruled out the possibility of an artefact due to buffers and solutions. Its significance remains enigmatic. Description: M.PHIL.

1995-01-01T00:00:00Z