Distribution of selenium-containing proteins in human serum.

Selenium-containing proteins in human serum of four volunteers in Beijing were separated and purified by preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Selenium contents in the proteins were quantified by high-performance liquid chromatography (HPLC) coupled with a fluorescence detector (FLD) after pretreatment with a microwave digestion system and derivatization with 2,3-diaminonaphthalene (DAN). Five selenium-containing proteins with apparent molecular weights (MWs) of 68+/-3, 57.5+/-2.5, 47+/-2, 41+/-1, and 21+/-1 kDa, respectively, were detected. By comparison with known data on serum selenium-containing proteins, the 68+/-3 kDa protein should belong to albumin, which took 6.3-9.8% of the total serum Se. The 57.5+/-2.5 kDa protein should be selenoprotein P and the 47+/-2 kDa protein was believed to be an isoform of selenoprotein P. The sum of Se in selenoprotein P and its isomer took about 41.1-69.3% and was the major form of human serum selenium. The 21+/-1 kDa protein should be plasma glutathione peroxidase (p-GPx) and its Se content was about 21.1-24.3%. Also, protein of 41+/-1 kDa should be a selenium-containing protein that, to our best knowledge, was reported for the first time. The Se percentage in this protein corresponded to 12.6-20.4% of total human serum Se.