Distribution of Se 75 in liver, kidney, and blood proteins of rats after intravenous injection of sodium selenite

After the injection of rats with Se 75 ‐labelled sodium selenite the distribution of Se 75 in proteins isolated from serum, liver supernatants, and kidney supernatants has been studied as a function of time. Shortly after injection, Se 75 became associated with a large number of proteins of the liver and kidney as shown by the distribution patterns obtained after chromatography on Sephadex G‐200. After longer periods the Se 75 became concentrated in only one or two peaks, and in this form was resistant to attack by a number of sulphydryl reagents and ascorbic acid. Only one major peak of Se 75 was found after gel filtration of serum proteins, and this was irrespective of the time since injection. Cellulose acetate or paper electrophoresis of labelled serum yielded only one band of Se 75 activity for all samples, but disc electrophoresis patterns varied considerably with time. It is suggested that one class of proteins, probably a‐globulins, is involved in Se 75 binding, and changes in Se 75 distribution occur within that class.