Speciation of selenium in the mammalian organism

As almost all of the selenium present in the mammalian organism is protein-bound, speciation is mostly concerned with the determination of the different selenium-containing proteins. Information on their distribution and their concentrations in the different tissues of the rat was obtained by means of tracer procedures which, after application of Se-75-selenite with a very high specific activity to selenium-depleted animals and electrophoretic separation of the labelled proteins, allow the determination of these compounds in the pmol to fmol range. A method was developed for the determination of selenocysteine and selenomethionine in the selenium-containing proteins. The identification of specific selenoproteins was achieved by analysis of their selenoamino acid residues and by studies on their characteristics and possible biological functions. This is being followed by the development of methods for the quantitative analysis of the selenoproteins in question in the tissues of animals and man. In this paper the strategies and procedures used in the identification, characterization and determination of the selenium species present in the mammalian organism will be discussed.