Selenoproteins in mitochondria and cytosol of Saccharomyces uvarum after growth in sodium selenite-supplemented media.

The extent of the biosynthesis of selenoproteins in mitochondria and cytosol of Saccharomyces uvarum depends on the sodium selenite concentration in the medium. In mitochondria there is a selenoprotein (SP 1) exhibiting glutathione peroxidase activity whose concentration already reaches a maximum at low concentrations of sodium selenite. A second selenoprotein (SP 2) was found in mitochondria and cytosol. Both proteins contain L-selenocysteine. The molecular masses of SP 1 and SP 2 are 73,000 Da and 83,000 Da, respectively. A subunit of SP 1 was found to have a molecular mass of 30,000 Da. SP 2, identified as a glycoprotein, has subunits with molecular masses of 36,500 Da and 5,000 Da. The selenium concentration of the total yeast increases from 260 micrograms/kg dry weight to 280 mg/kg dry weight after supplementation of the medium with sodium selenite.