Synthesis of [75Se]selenoproteins is greater in selenium-deficient sheep

Three Se-deficient and three Se-sufficient sheep with mean erythrocyte glutathione peroxidase activities of 30 and 249 mumol NADPH oxidized.min-1.g hemoglobin-1, respectively, were each labeled intraperitoneally with 555 MBq of sodium [75Se]selenite. All animals were killed and necropsied after 7 d. Peak plasma radioactivity occurred from 1 to 3 h post-labeling. Radioactivity in plasma associated with [75Se]selenoproteins was significantly higher in the Se-deficient sheep than in the Se-sufficient sheep 3 and 6 d after isotope administration. SDS-PAGE analysis of plasma followed by autoradiography indicated five selenoproteins, all of which were present in both groups. The molecular weights were 21.0, 23.0, 48.0, 55.5 and > 100 kDa. The protein with a mass of 55.5 kDa accounted for > 40% of the total radioactivity in both groups of sheep. Nine selenoproteins with molecular weights of 15.7, 18.8, 22.9, 26.8, 37.3, 42.4, 56.1, 62.7 and 71.3 kDa were detected in extracts from a range of tissues. Liver, kidney, heart and pituitary retained more radioactivity than the other tissues examined and the total amount of protein-associated 75Se in the liver, kidney and pituitary of Se-deficient sheep was significantly greater than that in Se-sufficient controls.