Biochemical studies on placental chorionic gonadotropin. I. Characterization of a high-molecular-weight gonadotropin in human chorionic tissues of the normal placenta.

Abstract

A high-molecular-weight glycoprotein which reacted with a specific antiserum to urinary human chorionic gonadotropin and with the gonadotropin receptor preparation from rat testes was detected in the extract of human chorionic tissues from the first trimester placenta of normal pregnancy and partially purified by ammonium sulfate fractionation followed by chromatographies on DEAE-Sephadex A-50 and Sephadex G-150. Its molecular weight was estimated to be 8.0×104 daltons by polyacrylamide gel disc electrophoresis in the presence of sodium dodecyl sulfate. In the presence of 2-mercaptoethanol, the major portion of this preparation was separated into alpha- and beta-subunits of rather high molecular weights compared to those of urinary human chorionic gonadotropin subunits by sodium dodecyl sulfate polyacrylamide gel disc electrophoresis. This preparation was shown to possess 2000 IU/mg of biological activity, and 2200 IU/mg of immunological activity, while its receptor binding capacity was equipotent to that of urinary chorionic gonadotropin. Chemical analyses, including amino acid and carbohydrate, were carried out. The present study suggests that high-molecular-weight type of human chorionic gonadotropin might be a complex of larger forms of alpha- and beta-subunits. This complex might be an intermediary component in the biosynthetic pathway of human chorionic gonadotropin or a product of posttranslational modification or a degradation product.