Might be responsible for some of the extracellular antioxidant defense properties of selenium or might be involved in the transport of selenium. May supply selenium to tissues such as brain and testis (By similarity). Passes from plasma into the glomerular filtrate where it is removed by endocytosis mediated by LRP2 in the proximal tubule epithelium. The C-terminus is not required for endocytic uptake in the proximal tubule epithelium. Phosphorylation sites are present in the extracellular medium. Belongs to the selenoprotein P family.