Abstract
Following injection with [75Se]selenite, a low molecular weight 75Se-selenocysteine containing protein was purified from rat muscle. The purification procedure involved ammonium sulfate fractionation, Sephadex G-50 gel filtration, cation exchange chromatography on CM-Sephadex, and reverse phase high pressure liquid chromatography using a C-18 Vydac column. Four forms of the protein were separated by the cation exchange and reverse phase chromatography steps. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry of the four proteins revealed masses of 9550 +/- 1, 9596 +/- 1.2, 9858 +/- 1.3, and 9898 +/- 1.1 daltons. Glutamate, glycine, lysine, leucine, and valine are the major amino acids in this protein. About 0.92 g atoms of selenium was found per g mol of protein, and this selenium was present as selenocysteine. Thus, this appears to be a new selenoprotein, and we have named it selenoprotein W.
Highlights
At present, there are only two mammalian selenoproteins with a known function
The present results indicate that thloew molecular weight selenium-containing protein from muscle should be considh sIn 50 v)
One is that the selenium appears to be present in stoichiometric amounts, and second, the selenium is present as selenocysteine
Summary
It converts damagingperoxides to the less harmful alcohols This selenoenzyme contains 4 g atoms of selenium/mol of protein (5, 6). The otherknown mammalian selenoenzyme is typeI iodothyronine 5‘deiodinase, which contains 1g atom of selenium/mol of protein (7, 8).Evidence has been presented for a number of other selenoproteins in mammaliantissues (9-11). Evidence for the presence of a low molecular weight selenium-containing protein in ovine muscle and heart was presented about 2 decades ago (14). The chemical form of selenium in glutathione peroxidase (18),type I 5’deiodinase (7), and selenoproteinP (12) has been shown to be selenocysteine The purpose of this communication is to present the purification and characteristics of this low molecular weight selenoprotein from rat muscle. The main radioactive eluant peak was pooled to exclude significant contamination by cytochrome c and concentratedby ultrafiltration
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