Unmasking by neuraminidase of specific chorionic gonadotrophin binding activity of human placental syncytiotrophoblast

Abstract

Purified human placental syncytiotrophoblast consistently failed to bind specifically to 125I-labeled hCG. Treatment of the syncytiotrophoblast with neuraminidase resulted in the ability to bind 125I-labeled hCG that was displaceable by excess of unlabeled hCG. Neuraminidase treatment removed 73.8% of the total neuraminic acid of the syncytiotrophoblast. The specific binding of 125I-labeled hCG increased linearly with increasing amount of neuraminidase-treated syncytiotrophoblast, was saturable and had a K(a) = 1.6 x 107 M-1. Excess of GH, prolactin, placental lactogen of insulin did not inhibit the binding, whereas LH did so completely and FSH partly.