The binding affinity and specificity of the estrogen receptor of the rat uterus and anterior pituitary.

Abstract

The soluble supernatant fractions of the uterus and anterior pituitary from ovariectomized adult rats contain 3H-17β-estradiolbinding proteins with identical sedimentation coefficients (8.6±0.2S). Using the Clark and Gorski estrogen receptor assay, the uterine estrogen receptor has a dissociation constant of 1.55×1O−9 (±0.07)M for 3H-17β-estradiol, which is essentially identical with the value of 1.40×10−9 (±0.11)M for the estrogen receptor of the anterior pituitary. The 17β-estradiol binding capacities of the uterus and anterior pituitary estrogen receptors are 0.56 and 0.24 pmole/mg of cell protein, respectively. However, on a per cell basis, the number of receptors in the uterine (∼16,000) or anterior pituitary cell (∼12,000) is of a similar order of magnitude. Estrogenic substances or estrogenic antagonists compete with 3H-17β-estradiol for binding to the receptors of both the anterior pituitary and uterus in the same sequence and to the same degree; that is, diethylstil bestrol≥ethynylestradiol>estrone≥estriol>CI-628>clomiphene. The pH optimum for 3H-17β-estradiol binding activity of the estrogen receptor is between 7 and 8. The decrease in binding activity as the pH is lowered or raised from the optimum is irreversible. The pH inactivation curves of the uterine and anterior pituitary estrogen receptor are the same. The similarities of the uterine and anterior pituitary estrogen receptors– molecular properties and their relationship to estrogen action in these tissues are discussed. (Endocrinology87: 987, 1970)