Purification of an estrophilic protein from calf uterus.

A method has been devised for purifying the estrogen-binding protein ("uptake receptor") of uterine cytosol which circumvents the marked tendency of this receptor to aggregate during attempted isolation. Ammonium sulfate precipitation of the estradiol-receptor complex of calf uterine cytosol in the presence of calcium ions yields both an 8S complex and its 4S subunit which are stable during further purification by gel filtration and ion exchange chromatography. The major product is the 4S complex which does not revert to 8S in the absence of salt and which has been purified about 2500-fold. The approximate isoelectric points of these partially purified 8S and 4S complexes are 5.8 and 6.4, respectively.