Purification and properties of selenoprotein W from rat muscle

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.