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Biomedical subjects

B Halliwell

Publications and source records attributed to B Halliwell.

At least 397 records · Page 22Linked to original sources
PubMed1981

Superoxide-dependent formation of hydroxyl radicals in the presence of iron salts. Detection of 'free' iron in biological systems by using bleomycin-dependent degradation of DNA.

Bleomycin in the presence of iron(II) degrades DNA to form a thiobarbituric acid-reactive product. This has been made the basis of a specific assay method for 'free' iron in biological fluids. Human synovial fluid, human cerebrospinal fluid and rat pleural-exudate fluid were found to contain micromolar concentrations of 'free' iron, which would be sufficient to allow formation of the hydroxyl radical from superoxide and hydrogen peroxide generated in vivo. This assay method does not detect iron bound to transport proteins or to enzymes.

Bleomycin↗
PubMed1981

The role of superoxide and hydroxyl radicals in the degradation of hyaluronic acid induced by metal ions and by ascorbic acid.

Purified commercial hyaluronic acid contains significant amounts of iron. Addition of Fe2+ to solutions of it causes depolymerization, which is inhibited by catalase and scavengers of the hydroxyl radical (. OH) but not by superoxide dismutase. Fe3+ is ineffective. Ascorbic acid also depolymerizes hyaluronic acid, apparently because it can reduce Fe3+ in the reaction mixtures to Fe2+. Ascorbate-induced depolymerization is inhibited by the specific iron chelator desferrioxamine, by catalase, and by scavengers of the hydroxyl radical. The relevance of these observations to rheumatoid arthritis and inflammatory joint diseases is discussed.

Arthritis, Rheumatoid↗
PubMed1981

Protection against superoxide and hydrogen peroxide in synovial fluid from rheumatoid patients.

1. On exposure of synovial fluid to superoxide and hydrogen peroxide, generated enzymically or by activated polymorphonuclear leucocytes, hyaluronic acid is depolymerized and the fluid loses its lubricating properties. The ability of synovial fluid from rheumatoid patients to scavenge superoxide and hydrogen peroxide was therefore examined. 2. Synovial fluid from a range of rheumatoid patients contained no superoxide dismutase activity, insufficient caeruloplasmin to scavenge any superoxide radical and little, if any, catalase activity. 3. Total ascorbate (reduced ascorbate + dehydroascorbate) concentrations in the plasma and synovial fluid of rheumatoid patients were similar in each case. The values are at the low end of the normal range. 4. These results are discussed in relation to the role of oxygen radicals in inflammatory joint disease.

Arthritis, Rheumatoid↗
PubMed1980

Effect of hydrogen peroxide on spinach (Spinacia oleracea) chloroplast fructose bisphosphatase.

Thiol-treated spinach (Spinacia oleracea) chloroplast fructose bisphosphatase (EC 3.1.3.11) is severely inhibited by H2O2, whereas the freshly purified enzyme is little affected. Dithiothreitol reverses inhibition by H2O2, indicating that essential thiol groups are oxidized during H2O2 inactivation. A new role for the dithiol and thioredoxin systems that are operative in illuminated chloroplasts is proposed.

Chloroplasts↗
PubMed1980

Action of calcium ions on spinach (Spinacia oleracea) chloroplast fructose bisphosphatase and other enzymes of the Calvin cycle.

Thiol-treated spinach (Spinacia oleracea) chloroplast fructose bisphosphatase is powerfully inhibited by Ca2+ non-competitively with respect to its substrate, fructose 1,6-bisphosphate. 500 microM-Ca2+ causes virtually complete inhibition and the Ki is 40 microM. Severe inhibition of sedoheptulose bisphosphatase is also caused by Ca2+. A role for Ca2+ in regulation of the Calvin cycle in spinach chloroplasts is proposed.

Calcium↗
PubMed1980

Properties of freshly purified and thiol-treated spinach chloroplast fructose bisphosphatase.

Freshly purified spinach chloroplast fructose bisphosphatase is powerfully inhibited by inorganic phosphate competitively with respect to its substrate fructose 1,6-bisphosphate. The concentrations of phosphate and substrate in the chloroplast stroma are such that the enzyme in this form could not operate at a significant rate in vivo. Incubation of the enzyme with dithiothreitol for 24 h decreases the Km for fructose 1,6-bisphosphate from 0.8 to 0.033 mM, decreases the Km for Mg2+ from 9 to 2 mM and substantially alleviates inhibition by inorganic phosphate. The physiological significance of thiol activation of the enzyme is discussed.

Chloroplasts↗
PubMed1979

Inhibition of the iron-catalysed formation of hydroxyl radicals from superoxide and of lipid peroxidation by desferrioxamine.

The peroxidation of membrane phospholipids induced in vitro by ascorbic acid or by dialuric acid (hydroxybarbituric acid) does not occur in the absence of traces of metal ions. Peroxidation induced by adding iron salts to phospholipids can either be promoted or inhibited by the chelators EDTA, diethylenetriaminepenta-acetic acid and bathophenanthrolinesulphonate, depending on the ratio [chelator]/[iron salt]. The iron chelator desferrioxamine inhibits peroxidation at all concentrations tested, and it also inhibits the iron-catalysed formation of hydroxyl radicals (OH.) from superoxide (O2-.). Since desferrioxamine is approved for clinical use, it might prove a valuable tool in the treatment of inflammation, poisoning by autoxidizable molecules and radiation damage.

Chelating Agents↗
PubMed1978

Subcellular localisation and identification of superoxide dismutase in the leaves of higher plants.

1. The subcellular location of superoxide dismutase in the leaves of spinach and other C3 plants has been investigated. 2. Most activity appeared to be located within chloroplasts. These organelles contain a cyanide-sensitive (copper-zinc) superoxide dismutase, most of which is located in the stroma although some is bound to the thylakoids. 3. Intact chloroplast fractions also contain a cyanide-insensitive (manganese) superoxide dismutase, but this activity is located on the outside of the chloroplasts and may be adsorbed onto them during isolation. 4. Leaf mitochondrial fractions contain only a small percentage of total leaf superoxide dismutase activity, but there is more than can be accounted for by contamination with chloroplasts. 5. Mitochondria contain both a cyanide-sensitive dismutase, apparently located in the intermembrane space, and a cyanide-insensitive activity, apparently located in the matrix. 6. The microsomal fraction contains no superoxide dismutase activity.

Chloroplasts↗
PubMed1978

Oxidation of 2-nitropropane by horseradish peroxidase. Involvement of hydrogen peroxide and of superoxide in the reaction mechanism.

Incubation of aqueous solutions of 2-nitropropane in air causes a slow oxidation reaction that generates H(2)O(2). Purified horseradish peroxidase catalyses the oxidation of such preincubated 2-nitropropane solutions according to the equation: [Formula: see text] The pH optimum is 4.5 and K(m) for 2-nitropropane is 16mm. Other nitroalkanes or nitro-aromatics tested are not oxidized at significant rates by peroxidase. H(2)O(2) or 2,4-dichlorophenol increases the rate of 2-nitropropane oxidation by peroxidase. Catalase inhibits the reaction completely. Superoxide dismutase or mannitol, a scavenger of the hydroxyl radical, OH(.), each inhibits partially. Aniline and guaiacol are also powerful inhibitors of 2-nitropropane oxidation. It is suggested that peroxidase uses the traces of H(2)O(2) generated during preincubation of 2-nitropropane to catalyse oxidation of this substrate into a radical species that can reduce O(2) to the superoxide ion, O(2) (-.).O(2) (-.), or OH(.) derived from it, then appears to react with more nitropropane, generating further radicals and H(2)O(2) to continue the oxidation. Inhibition by aniline and guaiacol seems to be due to a competition for H(2)O(2).

Alkanes↗
PubMed1978

Biochemical mechanisms accounting for the toxic action of oxygen on living organisms: the key role of superoxide dismutase.

It seems that superoxide dismutase plays the key role in protecting aerobes against O2 toxicity, but there is a whole range of ancillary mechanisms: enzymes to remove H2O2 (catalase, peroxidases) and hence to control formation of .OH from O2, which requires H2O2; antioxidants (ascorbate, GSH, alpha-tocopherol, carotenoids), which also react with singlet oxygen and/or .OH and often inhibit lipid peroxidation and last, but not least in animals, glutathione peroxidase, which controls the rate of lipid peroxidation. These mechanisms cope well at normal O2 concentrations but are insufficient at higher levels.

Aerobiosis↗