A receptor preparation from testes of Salmo gairdneri (Richardson): in vitro binding studies with 125I-labeled hCG and trout pituitary proteins.

A gonadotropin-receptor preparation from trout during full spermatogenesis known to bind 125I-hCG was used to test the ability of trout pituitary proteins to dislocate hCG from the receptors. From the proteins of male trout pituitaries chromatographed on immobilized concanavalin A, only the glycoprotein fraction was able to compete with hCG for the receptors. Unabsorbed proteins eluting in three fractions were radioiodinated and used as ligands. The fact that they were not taken up specifically by the receptor preparation, and the competition of the glycoproteins with 125I-hCG, is discussed in the context of the vertebrate's gonadotropic hormone system.