An external-sample liquid scintillation counting for Se-75 and its application to selenoprotein detection

An external-sample liquid scintillation (LS) counting for the gamma emitter Se-75 has been developed. An expressly designed well-type LS vial and a 2, 5-diphenyoxazole-1,4-bis(5-phenyl-2-oxazoyl)-benzene-xylene solution contai ning 35% tertrabutylzinn allow Se-75 to be counted in a standard LS counter with counting efficiency up to 43.2%, much higher than that of conventiona l LS counting method. This external sample LS has a good count rate lineari ty and exhibits low background count rates. After in vivo labeling with [Se-75]selenite, Se-75 distributions and the Se -containing proteins present in tissues of male rat were investigated by me ans of sodium dodecyl sulfate-polyacrylamide gel electrophoresis, external- sample LS and gamma -detector. Eight Se-containing proteins or protein subu nits were detected to be Se-containing proteins or protein subunits in arte rial wall, and their apparent molecular masses (Mr) were 76.4, 67.0, 57.4, 30.3, 25.4, 22.7, 21.7, and 15.1 kDa, respectively. In addition, eight Se-7 5-labeled proteins (Mr: 66.8, 57.0, 43.1, 30.0, 24.8, 19.8, 18.0, and 14.8 kDa) were found in brain homogenates, and nine 75Se-labeled proteins (Mr: 1 17.0, 78.0, 66.6, 57.2, 43.0, 38.1, 25.0, 20.1, and 18.0 kDa) were detected in testis homogenates. Some of them should be new biologically important s elenoproteins that have not been identified so far.