Abstract
The purpose of this study is to determine the affinities and the binding radicals of progesterone receptor, and their effect on the formation of the progesterone-receptor complex which binds to chromatin.
The uterine cytosol and the uterine chromatin were obtained from the estrogen primed immature female rabbit. 8S components were obtained after the 5-20% sucrose linear gradient centrifugation of uterine cytosol.
1. A sedimentation profile of the progesterone binding macromolecule showed that 3H-progesterone formed 8S and 5S binding complex, and the 3H-progesterone-8S binding was effectively inhibited by norethindrone or ethynodiol diacetate, resulting in the relative increases of 3H-progesterone-5S binding and free progesterone.
The effect of steroids on progesterone-8S binding was studied by a double reciprocal plot which showed that the following steroids were competitive inhibitors for progesterone 8S binding, and the order of the affinity for progesterone receptor was norethindrone (Ki=2.3×10-9M) >5α-dihydronorethindrone (Ki=6.0×10-9 M) > norethindrone acetate (Ki=8.8×10-9M) > lynestrenol (Ki=9.7×10-9M) >17α-ethynyl-4-estren-3β, 17β-diol (Ki=5.4×10-8M) > ethynodiol diacetate (Ki=1.3×10-7M), when taken from Ki. Ki (inhibitor constant) was calculated by the following equation : Ki=iKd/ (Kp-Kd), where Kd is the dissociation constant, i is the concentration of an inhibitor and Kp is the pretending dissociation constant in the presence of an inhibitor.
These results suggest that the 3-ketone and 17β-hydroxyl groups, and the plane of ring A/B of norethindrone are important to bind with progesterone receptor.
2. The uterine cytosols, preincubated with 3H-progesterone (or 3H-norethindrone) alone or in the presence of cold steroids at 4°C for lh 30 min, were incubated with uterine chromatins at 4°C for 1h 30 min. These chromatins were washed, and the radioactivities in them were counted.
It was indicated that the effect of cold steroids of the estrane series on the formation of progesterone- or norethindrone-receptor complex which binds to the chromatin appeared to be similar in their effect on progesterone- or norethindrone-receptor binding.
