Detection of small selenium-containing proteins in tissues of the rat

The important role of selenium in the mammalian organism has been manifeste d by the detection of several selenoenzymes, and there are still numerous s elenium-containing proteins to be identified. After in vivo labeling of rat s with [Se-75]-selenite, gel electrophoretic separation of the proteins in tissue homogenates and autoradiography of the labeled bands, information on the selenium-containing proteins present in the different tissues was obta ined. In the separation by SDS-PAGE and two-dimensional IEF/SDS-PAGE a larg e number of selenium-containing proteins or protein subunits with apparent molecular masses in the range from 116 to 8 kDa could be distinguished. Thi s range was extended by applying a modified Tricine-SDS-PAGE, which allows the determination of smaller proteins. Using this method in the separation of the homogenates of the adrenal, brain, diaphragm, epididymis, heart, kid ney, liver, lung, pituitary, prostate, skeletal muscle, spleen, thymus and thyroid, four additional selenium-containing proteins with molecular masses of approximately 7 kDa, 5kDa, 4 kDa and 3kDa were detected. The 5 kDa prot ein and the 7 kDa protein were identified as selenocysteine-containing sele noproteins.