[Assay of activated form of progesterone receptor with ATP-sepharose column chromatography]

Biological actions of progesterone are correlated with the ability of the progesterone receptor(PR) to bind to nuclear acceptor sites. Measurement of not only the presence of PR in a tissue but also the amount of that receptor which is able to bind to nuclear acceptor sites is important in predicting tissue response to progesterone. Activation of PR is required for effective binding to chromatin. Since the dextrancoated charcoal assay does not distinguish between an activated and a non-activated receptor, a rapid, relatively simple assay is needed which can account for an activated form of PR. Therefore, ATP-Sepharose column chromatography was tested to identify an activated form of PR. PR in crude uterine cytosol from estrogen-primed immature rabbits was labeled with 3H-progesterone at 0 degree C. The labeled PR was then incubated at 4 degrees C with uterine chromatin from ovariectomized mature rabbits. The freshly prepared PR had little capacity to bind to the chromatin. After activation manipulation at low temperature, low ionic strength and neutral pH, this PR was able to bind to chromatin approximately fourfold more than that activated by heating at 25 degrees C. The affinity of the activated and the non-activated PR for ATP was evaluated on ATP-Sepharose column chromatography. The activated PR was selectively adsorbed onto columns of ATP-Sepharose, and the binding ability of the activated PR to ATP paralleled that of the rabbit uterine chromatin. These results suggest that ATP-Sepharose column chromatography could be useful to identify an activated PR as a substitute for chromatin binding assay.