Selenoprotein P. A selenium-rich extracellular glycoprotein.
Selenoprotein P is a glycoprotein that has been purified from rat and human plasma. In selenium-replete rats it contains 65% of the plasma selenium and its concentration is 25-30 mg protein/L. In selenium-deficient rats its concentration is < 3 mg protein/L. The plasma half life of 75Se in selenoprotein P is 3 to 4 h, indicating a rapid turnover. Purified rat selenoprotein P contains 7.5 +/- 1 selenium atoms per molecule as selenocysteine. The sequence of the cloned cDNA predicts 10 selenocysteine residues, which suggests that the protein in plasma is a modification of the predicted one. Deduced amino acid sequence identity between rats and humans is 72%. The 3' untranslated region of selenoprotein P cDNA contains two predicted stem loops of the type essential for selenocysteine incorporation. Northern analysis indicates that selenoprotein P is expressed by many tissues. Hepatic selenoprotein P mRNA level, but not its transcription, decreases during selenium deficiency. The decrease is less than the decrease of glutathione peroxidase mRNA, however. Selenoprotein P is postulated to serve as an extracellular oxidant defense because its presence correlates with selenium protection of selenium-deficient rats against diquat-induced lipid peroxidation and liver necrosis. More research will be required to test this hypothesis and to establish the biochemical function of selenoprotein P.
Burk
R F
RF
Department of Medicine, Vanderbilt University School of Medicine, Nashville, TN 37232.
Hill
K E
KE
D000595:Amino Acid Sequence; D000818:Animals; D006801:Humans; D008969:Molecular Sequence Data; D011506:Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000502:physiology; D051149:Selenoprotein P; D051140:Selenoproteins
D011506:Proteins; D051149:Selenoprotein P; D051140:Selenoproteins