Selenoprotein P (SeP) is an extracellular,monomeric glycoprotein containing up to 10 selenocysteine residues in the polypeptide chain. It is ubiquitously expressed in mammalian tissues,and in human plasma it accounts for at least 40% of the total selenium concentration. SeP binds to heparin and cell membranes,and is associated with endothelial cells. SeP in human plasma protects against peroxynitrite-mediated oxidation and reduces phospholipid hydroperoxide in vitro,in accordance with the presumption that it has a function as an extracellular oxidant defense. Immunochemical assays have demonstrated that its concentration in plasma varies much with selenium intake,but other factors also have an influence.
