IN-VITRO EXPRESSION OF A MOUSE-TISSUE SPECIFIC GLUTATHIONE-PEROXIDASELIKE PROTEIN LACKING THE SELENOCYSTEINE CAN PROTECT STABLY TRANSFECTED MAMMALIAN-CELLS AGAINST OXIDATIVE DAMAGE

The complete sequence of the mouse epididymal protein (MEP24) was clon ed. It contains a 663 bp open-reading frame that, after conceptual tra nslation, shows extensive identity with proteins belonging to the glut athione peroxidase (GPX) family. However, a major difference between G PX5 (MEP24) and other known GPXs concerns a protein domain known to be critical for GPX function. To find out what could be the physiologica l function of such a protein in the mouse epididymis, we have used a m ammalian expression system to overexpress the GPX5 protein. Cells cons titutively expressing the GPX5 protein were generated and assayed for their ability to metabolize regular substrates of GPX enzymes. Data pr esented here show that the GPX5-expressing cells can metabolize hydrog en peroxide in a manner that is consistent with a peroxidase activity. However, the substrate preference of the GPX5-expressing cells and th eir apparent insensitivity to a regular inhibitor of GPX enzymes sugge st that the GPX5 protein belongs to a particular class of GPX proteins . Involvement of this protein in the physiology of the mouse epididymi s is discussed.