Abstract
A transplantable tumor CUB-II, a subline derived from the Dunning R 3327 rat prostatic adenocarcinoma, contains a unique sex steroid-binding protein. The protein possesses binding sites for androgens as well as for estrogens, and the binding affinity to androgen is higher than that to estrogen. The sedimentation coefficient of the protein is 10S. Sodium thiocyanate inhibits the binding to both sex steroids. This type of binding is not present in the 0.4 M KCl extract of nuclei. These results suggest that the binding protein is not the receptor for steroid hormones in spite of its high affinity binding to androgens and estrogens. Since the original tumor does not contain such protein, production of this binding protein seems to take place during culture in vitro and/or serial transplantations of the tumor.
