[Biochemical study on the thyrotropic activity in urinary immunoreactive-human chorionic gonadotropin of patients...

We have studied the biochemical properties of urinary immunoreactive-human Chorionic Gonadotropin (IR-hCG) using the human thyroid gland in vitro slice method to investigate the thyrotropic activity in purified IR-hCG of patients with thyroid hyperfunction associated with trophoblastic disease. IR-hCG was extracted using a kaolin-acetone-alcohol concentration and purified by DEAE Cellulose, Sephadex G-100 and DEAE Sephacel column chromatographies according to Nishimura et al. with slight modifications. The substance with thyrotropic activity (hCT) was found in 3 cases of trophoblastic disease with hyperthyroidism among the 14 cases investigated. HCT consists of two dissimilar subunits, namely, hCT alpha-subunit and hCT beta-subunit like hCG, whose molecular weights are estimated at about 15,000 and 20,000 respectively and have carbohydrate moiety bound to concanavalin A. The thyrotropic activity was shown by the recombinant hybrid molecules, hCT beta-subunit and hCG alpha-subunit, whereas no potency was found in hCT beta-subunit only. The carboxyterminal residues of hCT (Ile-Leu-Pro-Glu) were not digested by carboxypeptidases Band Y. These results suggest that hCT is an intrinsic activity of hCG and cross-reacts immunologically, while the amino acid residues of the carboxyterminus of the hCT beta-subunit are different from those of the hCG beta-subunit.