*7.1. SOD*

McCord and Fridovich, by discovering SOD, showed that this enzyme could defend cells exposed to O2 as a defense mechanism [86]. To counteract O2 •−, SOD is the first enzyme to convert this free radical to H2O2 [92–94]. Based on specific cofactors and cell locations, there are three different isoforms of SOD. These isoforms include cytosolic (SOD1 or Cu/ZnSOD), mitochondrial SOD (SOD2 or MnSOD), and extracellular SOD (SOD3 or ecSOD) [16].

SOD1 consists of both copper and zinc ions, which are responsible for maintaining enzymatically active sites. SOD1 does this by working with the remaining imidazolate ligands of the histidine SOD1. On the other hand, zinc ions are responsible for stabilizing enzymes in different cells of the body. It has also been estimated that the nuclear part of mammalian cells, cytoplasm, peroxisomes, lysosomes, chloroplasts, and cytosols host SOD1. However, the highest SOD1 activity has been reported in the human liver [91]. The second cofactor of SOD is MnSOD, which has the most increased activity in the renal cortex, and mainly peroxisomes and mitochondrial matrix are the enzyme sites [95]. The third cofactor (EC-SOD) is also present in human lymphocytes and plasma. Zinc and copper are found in this enzyme and effectively remove O2 •− from tissues [96].
