Table 1.

Types and characteristics of SOD.

Types	Location	Metal Cofactors	Combination
SOD1 (Cu/ZnSOD)	Cytoplasm, mitochondrial membrane space, and others (nucleus, lysosomes, and peroxisomes)	Cu2+ (catalyzing type) Zn2+ (stable form)	The two subunits are mainly combined by hydrophobic and electrostatic interactions; copper and zinc form coordination bonds with the histidine side chain on the active site.
SOD2 (MnSOD)	Mitochondrial matrix	Mn3+ (catalyzing type)	The manganese ion is coordinated with three histidine side chains, an aspartic acid side chain, and a water molecule or hydroxyl group (depending on the oxidation state of manganese).
SOD3 (EC-SOD)	Extracellular matrix, cell surface, and extracellular fluid	Cu2+ (catalyzing type) Zn2 + (stable form)	The active sites of Mn-SOD and Fe-SOD have the same type of amino acids coordinated with metal ions.