Characterization of a second estrogen receptor species in chick oviduct

Scatchard analysis of estradiol binding to chick oviduct cytosol is consistent with the existence of two high-affinity estrogen receptors which bind this ligand with equilibrium dissociation constants (Kd) of 0.06 and 0.8 mM. While the higher affinity receptor has been characterized and purified [Smith, R. G., & Schwartz, R.J. (1979) Biochem. J. 184, 331-343], the properties of the lower affinity receptor have not previously been defined; thus, its existence has been questioned. We now report the separation of the two receptors by low-capacity affinity chromatography, by sucrose density gradient centrifugation, and the partial separation by diethylaminoethyl ion-exchange chromatography. The former utilizes differences in estrogen binding kinetics associated with each receptor; the rate of dissociation (k-1) of [3H]estradiol from each receptor is identical (k-1 = 7.7 X 10(-5) s-1) while rates of association (k1) reflect the 10-fold differences in Kd. The lower affinity receptor has a k1 = 1.63 X 10(5) M-1 s-1, and the higher affinity receptor has a k1 = 1.33 X 10(6) M-1 s-1. The lower affinity receptor sediments at 3.5 S on sucrose density gradients compared to 4.2 S for the high-affinity form; it has high specificity for estrogen and is tissue specific, and its nuclear occupancy is associated with increases in ovalbumin gene transcription; thus, this macromolecule meets the criteria of an estrogen receptor. Augmentation of this receptor is possible by treatment of the cytosol with ATP/Mg2+, illustrating the existence of a non-steroid binding species.(ABSTRACT TRUNCATED AT 250 WORDS)