Effect of solubilization of porcine thyrotropin (TSH) receptor on TSH binding and on radio-receptor assay for anti-TSH receptor antibodies

The effect of solubilization of porcine thyrotropin receptor (TSHR) on TSH binding and on the radio-receptor assay for anti-TSHR antibodies was examined. After TSHR solubilization with 1% dodecylpolyethyleneglycoether, TSH binding affinity was increased, from Kd = 1.15nM to 0.45nM, and TSH binding capacity was slightly increased, from 0.15nM to 0.19nM. With a particulate membrane suspension from thyroid cells, blocking of TSH binding to the membrane suspension by anti-thyrotropin receptor antibody was observed only for thyroid stimulation blocking antibody (TSBAb), not for thyroid-stimulating antibody (TSAb). After the solubilization of TSHR, both TSBAb and TSAb blocked TSH-binding to the solubilized TSHR We speculate that TSAb interacts with the TSHR in the native conformation without interfering with TSH binding, and that after the solubilization, any anti-TSHR antibody interferes with TSH-binding due to the conformational change in TSHR. With these particulate thyroid cell membrane preparations, we can detect only TSBAb by the radio-receptor assay. (C) 1998 Academic Press.