Human serum does not contain a high affinity estrogen-binding glycoprotein different from sex hormone-binding...

The mannoglycoprotein fraction obtained by Concanavalin-A chromatography of human serum binds both androgens and estrogens with high affinity. Sex hormone-binding globulin (SHBG) is a component of this fraction that binds both steroids, but the fraction may contain another component that binds only estrogen. We used several chromatographic methods to ascertain whether the estradiol-binding properties of the mannoglycoprotein fraction could be attributed to SHBG or to SHBG and the putative estrogen-binding protein. DEAE-trisacryl, chromatofocusing, and anti-SHBG-immunoglobulin Sepharose chromatography resulted in coelution of the androgen- and estrogen-binding activities. SHBG purified by ligand affinity chromatography as well as immunoaffinity-purified SHBG had estradiol-binding properties similar to those of the crude mannoglycoprotein preparation. These data strongly suggest that 1) SHBG is the only estradiol-binding protein in the mannoglycoprotein fraction obtained by Concanavalin-A chromatography of human serum, and 2) the putative estradiol-binding protein of serum is most likely SHBG.