Antioxidants catalase

At the same time the interaction of superoxide with MPO may affect a total superoxide production by phagocytes. Thus, the superoxide adduct of MPO (Compound III) is probably quantitatively formed in PMA-stimulated human neutrophils [223]. Edwards and Swan [224] proposed that superoxide production regulate the respiratory burst of stimulated human neutrophils. It has also been suggested that the interaction of superoxide with HRP, MPO, and LPO resulted in the formation of Compound III by a two-step reaction [225]. Superoxide is able to react relatively rapidly with peroxidases and their catalytic intermediates. For example, the rate constant for reaction of superoxide with Fe(III)MPO is equal to 1.1-2.1 x 1061 mol 1 s 1 [226], and the rate constants for the reactions of Oi and HOO with HRP Compound I are equal to 1.6 x 106 and 2.2 x 1081 mol-1 s-1, respectively [227]. Thus, peroxidases may change their functions, from acting as prooxidant enzymes and the catalysts of free radical processes, and acquire antioxidant catalase properties as shown for HRP [228] and MPO [229]. In this case catalase activity depends on the two-electron oxidation of hydrogen peroxide by Compound I. 

Keywords Antioxidants Catalase Chronic leg ulcer Glutathione peroxidase... 

Two classes of antioxidants are known the low-molecular weight compounds (tocopherols, ascorbate, -carotene, glutathione, uric acid and etc.) and the proteins (albumin, transferrin, caeruloplasmin, ferritin, etc.) including antioxidant enzymes (e.g. superoxide dismutase, catalase, glutathione peroxidase). 

Normally, these reactive species are destroyed by protective enzymes, such as superoxide dismutase in mitochondria and cytosol and catalase in peroxisomes, but if a tissue has been anoxic the respiratory chain is very reduced and reoxygenation allows dangerous amounts to be formed. Muscle also contains significant quantities of the dipeptide, camosine ((J-alanylhistidine) (10—25 mM). The functions of camosine are obscure although it has been suggested to be an effective antioxidant (Pavlov et al., 1993). 

The heart has a relatively low catalase activity, which, together with the superoxide dismutase (SOD) system, acts to remove hydrogen peroxide and superoxide radicals. In addition, in man, dietary vitamin C plays an important role in the reduction of vitamin E, an intrinsic antioxidant component of biological membranes (Chen and Thacker, 1986 Niki, 1987). Both vitamins C and E can also react directly with hydroxyl and superoxide radicals (HalliwcU and Gutteridge, 1989 Meister, 1992). 

A number of studies have demonstrated protection against ethanol-induced gastric mucosal damage with several antioxidants, including SOD, catalase, allopurinol, DMSO, thiourea, dimethylthiourea, propylgallate and sulphydryl-containing substances, such as cysteine and... 

However, this will also prevent the formation of other cytotoxic species such as the hydroxyl radical. Further evidence that antioxidants prevent against the development of I/R injury comes from studies that show that previous ischaemic injury in the small intestine of rats results in prevention of further damage on subsequent ischaemic challenge in association with measured increases in mucosal glutathione peroxidase and catalase (Osborne et al., 1992). 

Hiraishi, H., Razandi, M., Terano, A. and Ivey, K.J. (1990). Antioxidant defenses of culture gastric mucosal cells against toxic oxygen metabolites. Role of glutathione redox cycle and endogenous catalase. Gastroenterology 98, A544. 

Future research should also focus its attention on the factors/mechanisms that regulate free-radical activity in vivo. The complex interrelationship between cellular and extracellular levels of antioxidants needs to be clarified, and factors that govern the synthetic rate of the scavenging enzymes, for example, SOD or catalase will provide further insight into cellular redox control. 

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