Rat iso-alpha1-fetoproteins purification and interaction with estradiol-17β

Abstract The combination of polyacrylamide gel electrophoresis and Concanavalin-A-Sepharose affinity chromatography has permitted the isolation on a preparative scale, of four molecular forms of rat alpha 1 -fetoprotein: a “slow” and a “fast” fraction, each separable into Concanavalin-A-adsorbed (“high carbohydrate”, i.e. rich in accessible αD-Mannosyl and αD-Glucosyl residues) and a Concanavalin-A-non adsorbed (“low carbohydrate”) fractions. These four iso-alpha 1 -fetoproteins (iso-AFP) bind estradiol-17β. However, they disclose differences in both their association constants and number of binding sites for this hormone. Very high affinity sites (10 9 ) are mainly located on the “slow-low carbohydrate” form. Low affinity, high capacity sites are preferentially located on the “high carbohydrate” form. These results confirm the molecular and functional heterogeneity of rat AFP and suggest that the carbohydrate moiety of the protein may have a role in estrogen-AFP interactions.