Steroid-protein interaction with particular reference to testosterone binding by human serum.

The binding affinity of serum protein for testosterone (and also of serum albumin as a reference protein) was determined by a technique based on the principle of equilibrium dialysis but with the use of the cross-linked dextran, Sephadex G-25, in a batchwise fashion on a semimicro scale. The binding parameters were shown to be dependent on the concentrations of both protein and steroid. The logarithm of the reciprocal of the protein concentration and the logarithm of the reciprocal of the bound steroid concentration (at 50% steroid binding) were in linear relationship. A sensitive and rapid method thus evolved for the detection and quantitative estimation of serum protein, or proteins, exhibiting a specific or high binding affinity for testosterone. This new technique, entailing a novel treatment of the experimental data, may also prove to be useful in the general study of steroid-protein interaction. Testosterone-binding levels in various human sera were determined in a comparative survey; markedly elevated levels were observed in advanced pregnancy.