An estrogen receptor in the liver of the viviparous watersnake, Nerodia; characterization and seasonal changes in binding capacity.

Understanding of steroid receptors is derived largely from the mammalian uterus and avian oviduct, and we have sought to characterize steroid receptors in relationship to natural cycles in subavian species. Here we report a putative estrogen receptor associated with the vitellogenic cycle in the female viviparous watersnake, Nerodia. Estrogen binding in cytosolic and nuclear hepatic cell extracts exhibits the following characteristics: high affinity (Kd, 1.3 X 10(-9) M cytosol; 5.7 X 10(-10) M nuclear extract), steroid specificity for natural estrogens, association time of 1 h at 22 C and 4 h at 0 C, and dissociation rate of 0.0268 min-1 at 0 C (half-time, 11.2 min) and 0.322 min-1 at 22 C (half-time, 0.906 min). Both cytosolic and nuclear estrogen binding are target organ specific; binding is low to undetectable in lung, skeletal muscle, and intestine and present in liver, oviduct, and kidney. A sedimentation coefficient of 6S was demonstrated in cytosol under low or high salt conditions, and a sedimentation coefficient of 3.5S was found in nuclear extract. Nuclear location of the receptor is indicated by extraction of increasing amounts of receptor by increasing KCl concentrations up to 0.5 M; 50% of the binding is extracted by 0.16 M KCl. Nuclear estrogen binding is increased significantly after estrogen injection. This estrogen-binding moiety is unusual, since it does not bind to the synthetic estrogen diethylstilbestrol, to antiestrogen clomiphene derivatives, or to calf thymus DNA-cellulose and diethylaminoethyl-Sepharose. Significant changes in cytosolic and nuclear hepatic estrogen receptor levels correlate with vitellogenic stage.