Subcellular distribution of selenium and Se-containing proteins in human liver

Selenium is an essential trace element in many living organisms. In the present paper, the subcellular distribution of selenium and Se-containing proteins in human liver samples, which were obtained from normal subjects who had an accidental death, was investigated by differential centrifugation and column chromatography. Selenium was mainly enriched in nuclei, mitochondria and cytosol. Almost half of Se existed in the nuclei due to their large amount in liver and high Se concentration. 15-30% of Se was found in small compounds with Mr<2000 in the liver components separated by dialysis. The average abundance of Se in small molecular mass species of whole-liver was 23.6%, which suggested most of Se associated with biological macromolecules. Eight kinds of Se-containing proteins with molecular mass of 335+/-20, 249+/-15, 106+/-11, 84.6+/-5.8, 70. 5+/-5.4, 45.6+/-1.5, 14.8+/-2.6, 8.5+/-1.2 kDa were found in the subcellular fractions of human liver. Among them the 335, 84.6 and 8. 5 kDa proteins were individually present in one subcellular fraction, whereas the others coexisted in two, three or four subcellular fractions. The most abundant Se-containing proteins, 70.5 and 14.8 kDa, accounted for 33.6% and 48.5% in the whole-liver soluble Se-containing protein, respectively. The former was enriched in cytosol and the latter was mainly present in nuclei and mitochondria.