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

The important role of selenium in the mammalian organism has been manifested by the detection of several selenoenzymes, and there are still numerous selenium-containing proteins to be identified. After in vivo labeling of rats with [75Se]-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 obtained. In the separation by SDS-PAGE and two-dimensional IEF/SDS-PAGE a large number of selenium-containing proteins or protein subunits with apparent molecular masses in the range from 116 to 8 kDa could be distinguished. This 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, kidney, 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 protein and the 7 kDa protein were identified as selenocysteine-containing selenoproteins.