ABSTRACT
In all living cells and tissues, there is a delicate balance between oxidizing compounds (oxidants) and reductants, called biological redox balance, which inuences many of the biochemical processes in the cell and ultimately determines the cell’s behavior. An excess on either side can lead to stress, either oxidative or reductive stress, if sufciently severe. The relevant oxidizing compounds are most commonly derived from molecular oxygen by partial reduction, and as they are relatively reactive they are grouped together under the imprecise term “Reactive Oxygen Species” (ROS). They can react subsequently with small molecules or ions containing heteroatoms such as nitrogen and halogens, for example, generating other reactive nitrogen or chlorine species. These groups of molecules, often called RNS and RClS, usually contain oxygen and are still oxidizing. As any one abbreviation for all of these reactive species is as vague as another, dening ROS as any reactive species formed from oxygen is what should be used, but only when the actual species involved is uncertain.
