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Science International Vol. 1 (5), 2013
Review Article
Biochemistry of Free Radicals and Oxidative Stress
Sabry M. El-Bahr
 
Abstract: Oxidative stress is caused by free radicals, Reactive Oxygen Species (ROS) which damage DNA, biomembrane lipids, proteins and other macromolecules. The primary source of ROS is leakage of electron from the respiratory chain during the reduction of molecular oxygen to water generating superoxide anion. ROS can be classified into oxygen centered radicals and oxygen centered non radicals. The oxygen centered radicals are superoxide anion (O•2), hydroxyl radicals (OH•) and alkoxyl radicals (RO•) and peroxyl radicals (ROO•). Oxygen centered non radicals are hydrogen peroxide (H2O2) and singlet oxygen (1O2). Other radicals species are nitrogen species such as nitric oxide (NO•), nitric dioxide (NO•2) and peroxynitrite (OONO―). ROS can be scavenged by the use of antioxidant system including non enzymatic components and a series of antioxidant enzymes. Non enzymatic components include glutathione, selenium, vitamin C and E. The antioxidant enzymes include glutathione peroxidase, catalase and superoxide dismutase which are the most major antioxidant enzymes that are capable to minimize oxidative stress in the organelles. The degree of lipid peroxidation is often used as an indicator of ROS mediated damage and the concentration of Malonaldehyde (MDA) in blood and tissues are generally used as biomarkers of lipid peroxidation. The mechanism of action of most of natural products and chemical drugs is done through the antioxidant properties of these drugs by reducing the lipid peroxidation and stimulation of enzymatic and non enzymatic antioxidant system within the organism. For instance, antioxidant properties of different natural product such as black cumin seed, curcumin, canola oil and plant combination can be evaluated by estimation of enzymatic and non enzymatic antioxidant level. Also, oxidative stress parameters as biomarker of metabolic diseases in equine whereas the preservation condition of spermatozoa in camel was also evaluated by determination of antioxidant capacity of the epididymal fluid. Importantly, many studies were exhibited in the oxidative stress era. However, this field of study still needs additional future researches at the molecular level.
 
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