Figure 2.

The process of ROS formation. Oxygen converts into superoxide radicals under the ROS-generated enzymes, and then consume hydrogen peroxide by superoxide dismutase (SOD). Hydrogen peroxide could be converted into water by glutathione peroxidase (GPX) instead of self-damage, or it can react with Fe-S proteins or heme to generate ferrous ion. Highly reactive hydroxyl peroxyl radicals produced by a Fenton reaction are destructive to cells. Besides, oxygen could produce LOOH company with the lipid in LOX, followed by converted into the LOH via GPX4, or LOOH can undergo a Fenton reaction to produce lipid peroxyl radicals. Ferrous ion and labile iron can be converted into ferric ions via lipid peroxides and hydrogen peroxides.