Combination of ectopic and standard human glycoprotein hormone alpha with beta subunits: discordance of immunologic and receptor-binding activity.

The beta subunit-combining properties of 2 purified ectopic alpha subunits have been compared to 10 different preparations of standard human alpha subunits (4 hCG-α, 3 hLH-α, 2 hFSH-α, 1 hTSH-α) by sensitive radioimmunoassay (RIA), radioreceptorassay (RRA), and gel chromatographic techniques. When combined with one preparation of hCG-β, hLH-α preparations generally had the highest combining activity and ectopic-α's the lowest activity, but there was overlap among groups and considerable variation among preparations from the same group. The degree of combination with hCG-β by RIA ranged from <1 to 120%, and by RRA from <1 to 78%. All combinations had higher activity in RIA than in RRA with RIA/RRA ratios of 1.4 to 60. Moreover, for each preparation the halftimes for maximal combination (t1) were shorter in RIA than in RRA, with t1 RIA/RRA ratios of 0.44 to 0.88. Five of the α's (3 standard, 2 ectopic) which were also combined with hLH-β showed results similar to those with hCG-β, both in RIA and RRA. Gel c...