An estrogen-binding component with a sedimentation coefficient of approximately 4S has been identified in the soluble fraction prepared from lung tissue obtained from human abortuses of 12–20 weeks gestational age. The proteinaceous nature of the estrogen-binding component was established from the findings of enzymatic degradation studies. Dihydrotestosterone and diethylstilbestrol had little or no affinity for the binding protein, whereas estriol and estrone competed with 17β- [3H]estradiol for binding. A 4S estrogen-binding component was also observed in fetal serum pretreated with dextran-coated charcoal to reduce the level of endogenous steroids. The serum estrogen-binding component differed from that of the lung tissue cytosol estrogen-binding macrornolecule(s) in specificity for steroid binding, i.e. in fetal serum dihydrotestosterone competed with 17β-[3H]estradiol for binding while estriol did not. Human fetal lung and kidney tissues contained the greatest amount of 17β-estradiol-binding activity of the tissues studied. Little or no estrogen binding was detectable in human fetal heart, brain, liver, or adrenal tissues.
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