Figure 3.

Cellular control of reactive oxygen species (ROS). (A) There are three intrinsic mechanisms to reduce ROS. Superoxide dismutase (SOD) is localized in different portions of the cell, with SOD1 (Cu/Zn-SOD) present in the cytoplasm and nucleus, SOD2 (Mn-SOD) present in the mitochondrial matrix, and SOD3 (Extracellular-Cu/Zn-SOD) located extracellularly. These manage ROS by reducing O₂^•− to H₂O₂. There are two methods to reduce H₂O₂. The first method is by catalase enzyme (CAT), which acts in a two-step reaction to remove two H₂O₂ and produce two water and one oxygen. The second method is glutathione and glutathione peroxidase (GPx). The reduced form of glutathione (GSH) is activated by GPx to convert two water molecules from H₂O₂. The oxidized form of GSH (GSSG) is replenished by glutathione reductase to remove future ROS. (B) Five antioxidant pathways are reviewed herein for their ability to assist in removing ROS. Cysteine is produced in the cytoplasm after cystine is transported through a cystine/glutamate antiporter (XCT). Cysteine contributes to the formation of γ-glutamylcysteine (GGC) after reacting with glutamate (Glu) produced by the mitochondria. Finally, GGC reacts with glycine (Gly) to form GSH. Cysteamine is important as it assists in the conversion of cystine to cysteine. Both cysteine and cysteamine feed into the production of hypotaurine. Hypotaurine reduces H₂O₂ to form water and taurine. However, hypotaurine may also produce H₂O₂ and peroxytaurine from O₂^•− and hydrogen. Zinc enters the cell through zinc transporters (ZnT) and contributes to the formation of SOD1 (Cu/Zn-SOD). Selenite is commonly included in cultures produced by IVP where it can enter the cell and produce selenide. Selenium is a cofactor for GPx. Created with Biorender.com.