Interplay between reactive oxygen and nitrogen species in living organisms

In living organisms most oxygen consumed is reduced to water via four-electron reduction. However, few percentages of oxygen are reduced by consecutive one electron mechanisms giving rise to superoxide anion radical, (O2 center dot- ), hydrogen peroxide (H2O2) and hydroxyl radical (HO center dot) and their derivatives collectively called reactive oxygen species (ROS). Nitric oxide (center dot NO) is produced at oxidation of arginine by nitric oxide synthase (NOS) or at reduction of nitrites by diverse reductases. Interaction of center dot NO with O2 center dot- results in formation of peroxinitrite (ONOO- ), a powerful oxidant. Additionally, H2O2 can interact with center dot NO resulting in HO center dot production. Nitric oxide and its derivatives are collectively called reactive nitrogen species (RNS) and together with ROS they form a group of so-called reactive oxygen/nitrogen species (RONS). Nonspecific effects of RONS are related to their interaction with various components of living organisms, whereas specific effects are based mainly on interaction with specific proteins containing [Fe-S]-clusters and thiol groups of cysteine residues. Most early ROS studies were mainly focused on their deleterious effects, whereas now more delicate mechanisms of their involvement in signaling and toxic processes are under inspection. Studies of RNS activities in biological systems started from their vasodilating effects which lead to discovery of activation of soluble guanylate cyclase. Interestingly, at low ROS and RNS concentrations signaling effects prevail, whereas at their high concentrations they affect biological systems inhibiting due to massive oxidation of cellular components.

Automated summary

In living organisms, most oxygen is reduced to water through four-electron reduction, but a small percentage is reduced through one-electron mechanisms to produce reactive oxygen and nitrogen species. These species interact with various components of living organisms, leading to diverse effects on biological systems.