Binding of progesterone with the oviduct cytosol fraction of estrogen-primed quail (Coturnix coturnix japonica).

Progesterone-specific binding components were detected in the cytosol fraction of enlarged oviducts from estrogen (diethylstilbestrol)-primed immature Japanese quail (Coturnix coturnix japonica) females by several techniques using [3H]promegestone. The oviduct as a target tissue of progesterone is the most efficient in [3H]promegestone binding, and muscle and intestine as nontarget tissues and plasma are less efficient as expected. By using [3H]promegestone for binding, the possibility of blood contamination of the oviduct may have been eliminated with the detection of a specific binding site. The participation of protein in the steroid-binding site was inferred from the destruction of the binding component by protease, but not by RNase or DNase. The interaction with [3H]promegestone in low salt conditions has a high affinity (Kd 0.69 nM) and low capacity (the number of binding sites per milligram of protein is about 1.3 pmol). Six unlabeled steroids were tested as competitors for binding to [3H]promegestone in vitro. Progesterone-like steroids competed specifically with [3H]promegestone: progesterone congruent to promegestone greater than deoxycorticosterone greater than testosterone much greater than estradiol-17 beta greater than cortisol. These chemical properties show that the progesterone binding protein present in the oviduct of estrogen-primed quail is essentially similar to that obtained from chick oviduct. In addition, heterogeneity of the [3H]promegestone binding components was shown. The binding component was eluted as an aggregate on gel (Bio-Gel A-0.5m) column chromatography in low salt conditions which reverted to two major peaks, tentatively named I (molecular weight, about 110,000) and II (about 41,000), in the presence of high salt (0.3 M KCl). The relative amounts of the two peaks differed. It was interesting that peak II of the small component was not found in the estrogen-primed chick and was a distinctive one in quail. On the other hand, both peaks were recovered with 0.3 M KCl elution on DEAE-cellulose column chromatography. These studies suggest that this binding component may function as a biological receptor for progesterone in the estrogen-enlarged oviduct, and the problems to be solved are under examination.