α-Subunit Conformation in Glycoprotein Hormones and Recombinants as Assessed by Specific Antisera*

Abstract

RIAs specific for the a-subunit of glycoprotein hormones were used to monitor the subunit conformation in ovine FSH and TSH and in recombinants of ovine LHa with (ovine and porcine) LHα and hCGβ. Differences in log-logit slopes of the RIA dilution curves were interpreted to indicate changes, presumably conformational, in the local environment of the antigenic determinants of the α-subunit. In all but one case, free ovine LHα yielded a slope that was distinct from those of the hormones and recombinants. FSH, TSH, and the homologous LH recombinant all exhibited different slopes, and the recombinant ovine LHα-hCGβ was characterized by a slope that was distinct from the identical slopes of the recombinants ovine LHα-ovine LHβ and ovine LHα-porcine LHβ. These results suggest that a conformational change occurs in the α-subunit upon association with a β-subunit and that different β-subunits may induce distinct conformations in a common α-subunit.