ABSTRACT
Institute of Microbiology, Bulgarian Academy of Sciences, 26 Academician Georgy Bonchev St., 1113 Sofi a, Bulgaria, Fax: +359 2 870 01 09, E-mail: jserkedjieva@microbio.bas.bg
Introduction
Reactive oxygen species (ROS) are continuously being generated under physiological conditions. They are involved in the cell growth, differentiation, progression and death. Low concentrations of ROS may be benefi cial or even indispensable in processes such as intracellular signaling and defense against micro-organisms. However, when the natural antioxidant defenses of the organism are overwhelmed by an excessive generation of ROS, a situation of “oxidative stress” occurs, in which cellular and extracellular macromolecules (proteins, lipids and nucleic acids) can suffer oxidative damage, causing tissue injury. The .OH radical is the most reactive product of ROS formed by successive l-electron reductions of molecular O2 in cell metabolism, and is primarily responsible for the cytotoxic effects observed in aerobic organisms extending from bacteria to plants and animals. Excessive free radical production originating from endogenous or exogenous sources has been implicated in several diseases, including cancer, diabetes and cardiovascular diseases, ageing etc. (Halliwell and Gutteridge 1990 and references cited therein).
