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

Abstract

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 [ 3 H]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 [ 3 H]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 tf the binding component by protease, but not by RNase or DNase. The interaction with [ 3 H]promegestone in low salt conditions has a high affinity ( K d 0.69 n M) and low capacity (the number of binding sites per miligram 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 [ 3 H]promegestone: progesterone ⋍ promegestone deoxycorticosterone>testosterone>estradiol-17β 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 tunction as a biological receptor for progesterone in the estrogen-enlarged oviduct, and the problems to be solved are under examination.