ABSTRACT
All aerobic cells produce reactive oxygen species (ROS) as an unavoidable consequence of their metabolism (Halliwell and Gutteridge 2007). Main sources include the four electron reduction of molecular oxygen to water coupled with oxidative phosphorylation, electron transport chains in mitochondria and microsomes, the activity of several enzymes that produce ROS as intermediates or final products, and immunological reactions such as active phagocytosis. The most commonly generated ROS are the singlet oxygen (1O2), superoxide anion (O2-), hydrogen peroxide (H2O2), and the hydroxyl radical (•OH), which rapidly combine to form other molecules, like peroxynitrite (HOONO), hypochloric acid (HOCl), peroxyl radicals (ROO•), and alkoxyl radicals (RO•). Although all these molecules are generally termed as ROS, they greatly differ in terms of cellular reactivity and potential to cause toxic insults to lipids, proteins, and DNA (Regoli and Winston 1999).
