Binding Affinity and Specificity of the Estrogen Receptor of the Rat Uterus and Anterior Pituitary

TLDR: 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); on a per cell basis, the number of receptors in the uterine or anterior pituitsary cell is of a similar order of magnitude.

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>estro...