Identification of a novel sex steroid binding protein.
We describe a cytoplasmic steroid binding protein in the chick oviduct which has intriguing characteristics. This protein binds [3H]estradiol with high affinity (Kd = 30 X 10(-9) M) and limited capacity (300 fmol/mg of cytosol protein). It sediments at 8 S in low-salt sucrose density gradients and at 4 S in high-salt gradients. Unlike the estrogen receptor, however, this protein also binds progesterone, R5020, testosterone, and 5 alpha-dihydrotestosterone with similar affinities and in a competitive manner. Moreover, it is not translocated to the nucleus by the in vivo administration of these sex steroids. The protein is only present in estrogen-responsive tissue, and like the sex steroid receptors, its synthesis appears to be regulated by estrogen.
D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism; D002645:Chickens; D003593:Cytoplasm / Q000378:metabolism; D004958:Estradiol / Q000378:metabolism / Q000494:pharmacology; D005260:Female; D007700:Kinetics; D010057:Oviducts / Q000032:analysis*; D011960:Receptors, Estrogen / Q000302:isolation & purification*; D012738:Sex Hormone-Binding Globulin / Q000378:metabolism*; D013329:Structure-Activity Relationship
D011960:Receptors, Estrogen; D012738:Sex Hormone-Binding Globulin; D004958:Estradiol