SOD3 is a member of the superoxide dismutase protein family. SODs are antioxidant enzymes that catalyse the dismutation of two superoxide radicals into hydrogen peroxide and oxygen. SOD3 is thought to protect the brain, lungs and other tissues from oxidative stress. It is secreted into the extracellular space and forms a glycosylated homotetramer that is anchored to the extracellular matrix and cell surfaces through an interaction with heparan sulfate proteoglycan and collagen. A small percentage of SOD3 is cleaved near the C-terminus before secretion to generate circulating tetramers that do not interact with the extracellular matrix.