Selenium and amino acid composition of selenoprotein P, the major selenoprotein in rat serum.
Selenoprotein P is the second plasma selenoprotein to be purified. It is a glycoprotein and has been shown to be distinct from plasma glutathione peroxidase. This study characterizes selenoprotein P further. Deglycosylation of the protein shifts its migration on sodium dodecyl sulfate-polyacrylamide gel electrophoresis from Mr 57,000 to Mr 43,000, indicating it has a substantial carbohydrate component. Measurement of selenium indicates a selenium content of 7.5 +/- 1.0 atoms/molecule based on a polypeptide weight of 43,000. Amino acid analysis accounts for all the selenium as selenocysteine. The protein is also rich in cysteine (17 residues) and histidine (23 residues). Fragmentation of selenoprotein P by trypsin and by cyanogen bromide produces peptides with varying selenium content. This indicates that selenium-rich regions of the protein exist. The concentration of selenoprotein P determined by radioimmunoassay in serum from control rats is 26.3 +/- 4.5 micrograms/ml and in serum from selenium-deficient rats it is 2.7 +/- 0.8 micrograms/ml. Depletion of selenoprotein P from control serum using an immunoaffinity column indicates that over 60% of serum selenium in the rat is contained in this protein. These results demonstrate that selenoprotein P is the major form of selenium in rat serum. It is the first selenoprotein described which has more than one selenium atom/polypeptide chain.
Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee 37232.
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Read
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Bellew
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Yang
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Hill
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Palmer
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Burk
D000596:Amino Acids / Q000032:analysis; D000818:Animals; D003488:Cyanogen Bromide; D004591:Electrophoresis, Polyacrylamide Gel; D006023:Glycoproteins / Q000097:blood / Q000737:chemistry / Q000302:isolation & purification; D008297:Male; D008970:Molecular Weight; D010446:Peptide Fragments / Q000302:isolation & purification; D011506:Proteins / Q000737:chemistry* / Q000302:isolation & purification; D051381:Rats; D011919:Rats, Inbred Strains; D012643:Selenium / Q000097:blood* / Q000737:chemistry* / Q000302:isolation & purification; D051149:Selenoprotein P; D051140:Selenoproteins; D014357:Trypsin
D000596:Amino Acids; D006023:Glycoproteins; D010446:Peptide Fragments; D011506:Proteins; D051149:Selenoprotein P; D051140:Selenoproteins; D014357:Trypsin; D012643:Selenium; D003488:Cyanogen Bromide