Binding of 17beta-estradiol by variants of alpha-fetoprotein in rat amniotic fluid

Two variants of alpha-fetoprotein in rat amniotic fluid were separated by their different affinity for concanavalin A-Sepharose, which selectively binds alpha-D-manno-pyranosides and alpha-D-glucopyranosides. Both forms had the same mobility upon polyacrylamide gel electrophoresis. The binding of 17beta-estradiol per mg of alpha-fetoprotein, determined both immunologically and electrophoretically, was the same for both variants. These results indicate that a specific carbohydrate portion of the molecule is not necessary for steroid binding.