An immobilized antiestrogen binds a specific uterine protein in addition to estrogen receptor proteins

An antiestrogen affinity resin was synthesized by conjugating LY117018, a benzothiophene -derived antiestrogen, to epoxy-activated agarose. This affinity resin bound the Mr = 50 000 and 65 000 estrogen receptor proteins of rabbit uterine cytosol; in addition, it retained a protein from the cytosols of both rat and rabbit uteri that exhibited an ability to interact specifically with LY117018. The possibility that the LY117018 binding protein, which is distinct from estrogen receptors, may play a role in the antiestrogenic actions of LY117018 is discussed.