Evidence for Specific Selenium Target Tissues and New Biologically Important Selenoproteins

After in-vivo labeling with [75Se]selenite the Se-containing proteins present in rat tissues were investigated by means of SDS-polyacrylamide gel electrophoresis. Thirteen Se-containing proteins or protein subunits with relative molecular weights of 12,100, 15,600, 18,000, 19,700, 22,200, 23,700, 27,800, 33,300, 55,500, 59,900, 64,900, 70,100 and 75,400 were detected in the tissue homogenates. The protein with the molecular weight of 23,700 was the subunit of glutathione peroxidase, which is the only selenoprotein so far known to have biological functions in animals. Most of these proteins were found in all tissues investigated but one was only detected in the testes and the spermatozoa and one was present mainly in the thyroid. With inadequate selenium intake there was a priority supply of the element to the brain, the reproductive and the endocrine organs, and at a molecular level to Se-containing proteins other than glutathione peroxidase. The results suggest important biological functions of these selenoproteins, especially in the specific target tissues.