Some commercial samples of bovine catalase contain superoxide dismutase activity. Therefore the inhibition of a reaction on the addition of a catalase preparation need not necessarily mean that H2O2 is responsible for the reaction.
Sulphasalazine (Salazopyrin) and its metabolites sulphapyridine and 5-aminosalicylate are powerful scavengers of the hydroxyl radical, determined by pulse radiolysis and confirmed by assays based on deoxyribose degradation by hydroxyl radicals. 5-Aminosalicylate can also protect α1-anti-protease against attack by the myeloperoxidase-derived oxidant hypochlorous acid. The ability to scavenge oxidants produced at sites of inflammation may contribute to the anti-inflammatory action of sulphasalazine and its metabolites.
There is now a large body of population studies showing that diets high in fruits and vegetables, i.e. foods rich in antioxidant compounds, are associated with a lower incidence of cardiovascular disease [1]; moreover, many in vitro and some in vivo studies have suggested that oxidative modification of low density lipoprotein is involved in the onset of atherosclerosis and exacerbates its clinical manifestations [2] … * Corresponding author
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The hydroxyl radical •OH is the most reactive species. The hydroxyl radical reacts at, or close to, a diffusion-controlled rate with all biological molecules, and its half-life in cells is estimated to be 10-9 sec. It is produced when water is exposed to ionizing radiation, fragmenting the oxygen-hydrogen covalent bond, leaving a single electron on hydrogen and one on oxygen. Most of the •OH generated in vivo, except during excessive exposure to ionizing radiation, probably comes from the metal ion-dependent breakdown of hydrogen peroxide (H2O2). Reactions of all these are important when considering the toxicological effects of metal poisoning, but only iron(II)- and copper(I)-dependent reactions could occur in vivo under normal conditions. The iron(II)-dependent formation of •OH is better known as the “Fenton reaction,” and it is far more complicated. There has been repeated controversy as to the formation of •OH in this reaction at physiological pH (7.4), because other iron-oxygen complexes are often postulated as alternatives.
1. Spinach (Spinacia oleracea L.) leaf extracts catalyse the oxidation of formate to CO2. 2. Two enzymic systems are responsible for this oxidation, the peroxidatic action of catalase (EC 1.11.1.6) and NAD-dependent formate dehydrogenase (EC 1.2.1.2). 3. Formate dehydrogenase is mainly, if not exclusively, located in the mitochondria. This enzyme has a pH optimum of 6–6.5 and a Km for formate of 1.7mm in the presence of 1 mm-NAD+. 4. Peroxidatic action of catalase is presumed to take place in peroxisomes, since these seem to be the subcellular site of catalase. Formate oxidation at pH5 by chloroplast and mitochondrial fractions is due to their ability to generate H2O2 and the presence of contaminating catalase. 5. During photorespiration, peroxidatic oxidation of formate by catalase can occur over a wide range of pH values, but the rate of this reaction is probably controlled by the concentration of formate present, to an extent dependent on the pH.
Free-radical attack upon uric acid generates allantoin [Ames, Cathcart, Schwiers & Hochstein (1981) Proc. Natl. Acad. Sci. U.S.A. 78, 6858-6862]. Methods are described for the accurate measurement of uric acid and allantoin in human body fluids. The concentrations of uric acid and allantoin in human serum and synovial fluid are reported. It is suggested that measurement of changes in allantoin concentration may be a useful index of free-radical reactions taking place in vivo.
