Alpha-subunit conformation in glycoprotein hormones and recombinants as assessed by specific antisera

RIAs specific for the alpha-subunit of glycoprotein hormones were used to monitor the subunit conformation in ovine FSH and TSH and in recombinants of ovine LH alpha with (ovine and porcine) LH beta and hCG beta. 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 alpha-subunit. In all but one case, free ovine LH alpha 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 LH alpha-hCG beta was characterized by a slope that was distinct from the identical slopes of the recombinants ovine LH alpha-ovine LH beta and ovine LH alpha-porcine LH beta. These results suggest that a conformational change occurs in the alpha-subunit upon association with a beta-subunit and that different beta-subunits may induce distinct conformations in a common alpha-subunit.