A Distinction between 3-Methylcholanthrene and Estrogen Binding in the Uterus

The binding of methylcholanthrene-³H to macromolecular components of the uterine cytosol fraction was analyzed and compared with the specific binding of estradiol to its receptor. Methylcholanthrene-³H binds to a component which sediments as a 5 S complex on sucrose gradients and can be easily distinguished from the 8 S estradiol-receptor complex. Unlabeled estradiol does not interfere with methylcholanthrene-³H binding, nor does unlabeled methylcholanthrene have any effect on the formation or sedimentation of the estradiol-³H-receptor complex. These results negate the possibility that the carcinogen acts in estrogenic target tissues by directly interfering with the normal interaction of estrogens with their receptor sites.