Binding of the chicken oviduct progesterone receptor to steroid affinity resins: resistance to elution with mercurial reagents.

Mercurial reagents rapidly and reversibly dissociated purified chick oviduct progesterone receptor-hormone complex in solution. However, batchwise incubation of steroid affinity resin-receptor complex with organic mercurials or HgCl2 resulted in release of less than 10% of the adsorbed hormone binding activity. Limited treatment of the affinity resin-receptor complex with mercurials did not reduce the amount of receptor that could be eluted by subsequent incubation with progesterone. Continuous flow elution with HgCl2 increased the percentage of receptor recovered; however, the major fraction remained resistant to mercurial treatment and was recovered upon subsequent elution with steroid. After purification by affinity chromatography, the mercurial-treated receptor, but not the hormone-receptor complex, bound to steroid affinity resin in a biospecific manner. Thus the effect of mercurials on hormone binding is more complex than deduced from studies performed on receptor in solution. The progesterone receptor may contain a second, low-affinity hormone binding site that is insensitive to mercurials. Alternatively, mercurials may not block hormone binding completely, but rather reduce the affinity so that binding can only be detected at high concentrations of hormone such as are present within the steroid affinity resin.