Transport of Cortisol-4-C¹⁴ and Progesterone-4-C¹⁴ by Serum Proteins as Demonstrated by Paper Electrophoresis and Paper Chromatography

¹ From the Protein and Steroid Section, Biochemistry Department, Army Medical Research Laboratory, Fort Knox, Kentucky

Interaction between low concentrations of cortisol-4-C¹⁴ or progesterone-4-C¹⁴ and serum proteins was investigated by paper-electrophoretic methods in human serum albumin solution as well as in human and rat serum. Between 2 and 10% of cortisol and between 70 and 90% of progesterone were found to be bound and thus transported by human albumin. Similar transport values were observed in paper-chromatographic studies in which the steroids migrated in aqueous solution, in the presence and absence of serum proteins. A critical evaluation was made on the use of paper-electrophoretic procedures in protein-binding studies. The demonstration of a firm albumin binding of progesterone, and a comparatively loose attachment of cortisol, is in general agreement with results obtained by ultracentrifugation and ‘free’ electrophoresis. Some physiological implications are mentioned.