This gene encodes a selenoprotein containing multiple selenocysteine (Sec) residues, which are encoded by the UGA codon that normally signals translation termination. The 3' UTR of selenoprotein genes have a common stem-loop structure, the sec insertion sequence (SECIS), which is necessary for the recognition of UGA as a Sec codon rather than as a stop signal. This selenoprotein is an extracellular glycoprotein, and is unusual in that it contains 10 Sec residues per polypeptide. It is a heparin-binding protein that appears to be associated with endothelial cells, and has been implicated to function as an antioxidant in the extracellular space.