Hormone binding modified endogenous proteolysis of LH/hCG receptors in rat ovarian plasma membranes.

Purified rat ovarian plasma membranes were subjected to incubation under conditions where luteinizing hormone receptors were either free or bound to hCG. When receptor proteolysis was followed by labeling the receptor with tritiated borohydride or [125I]hCG, occupied receptors were found to be more accessible to endogenous proteinases than unoccupied receptors. They exhibited greater rates of degradation and also produced an additional degradation product upon proteolysis. Degradation of other plasma membrane (glyco)polypeptides, however, was not affected by hormone binding. These results indicate that hCG binding induces a conformational or a structural change in its receptor, thereby increasing its susceptibility to endogenous plasma membrane proteinases.