Large molecular species of chorionic gonadotrophin from human placental tissues: biosynthesis and physico-chemical properties

Abstract

Abstract. Human placental tissues in the first trimester of pregnancy were maintained in organ culture and incubated with [3H]proline for 90 min at 37°C. The tissues were homogenized with a protease inhibitor in the buffered medium and separated into subcellular components. A large molecular protein which reacted with antiserum to hCG hCGα and hCGβ, and with the receptor membranes obtained from bovine corpus luteum, was detected in the microsomal component and post-microsomal supernatant fraction. This protein was purified by chromatography on Sephadex G-100, Sepharose-6B and DEAE-Sephadex A-50. The large molecular species of hCG contained high radioactivity and was immunoprecipitated with all three antisera. The purified large molecular hCG was analyzed by electrophoresis on sodium dodecyl sulphate (SDS) polyacrylamide gel. Its molecular weight was estimated to be 90000 daltons. When the large molecular hCG was treated with 8 m urea and mercaptoethanol in the presence of SDS, a major portion of the material dissociated into immunoreactive α and β subunits of rather high molecular weights compared to standard hCG subunits. Under similar conditions standard hCG dissociates completely into its subunits. The present results suggest that the large molecular species of hCG might be a complex composed of larger forms of α and β subunits. This complex might be an intermediary component in the biosynthetic pathway of hCG or a product of posttranslational modification.