POSSIBLE BINDING-SITE OF THYROTROPIN BINDING INHIBITOR IMMUNOGLOBULIN (TBII) ON THE THYROTROPIN (TSH) RECEPTOR, WHICH IS DIFFERENT FROM TSH BINDING-SITE

A synthetic decapeptide, P-194, which has the sequence No. 103 to 111 of hTSH receptor structure with an additional N-terminal tyrosine, did not bind TSH nor affected its receptor binding and thyroid stimulating activity. Preincubation of P-194 with sera from thyroid patients caused a significant decrease in TBII activity in almost all 12 TBII positive sera and an increase of thyroid stimulating activity in 3 of 7 Graves' IgG studied. In addition, [125I] P-194 bound to serum IgG fraction from thyroid patients with a positive correlation with TBII (N=35, r=0.509, p<0.01). The P-194 portion may be, at least a part of, TBII binding site distinct from the TSH binding site on the TSH receptor. © 1990.