title: Characterization of GnRH receptors in bovine pituitary membranes.
abstract: Bovine pituitary gonadotropin-releasing hormone (GnRH) receptors were characterized and identified utilizing a superactive GnRH analog, Buserelin [( D-Ser(t-Bu)6, des-Gly10-ethylamide]-GnRH), and a photoreactive GnRH analog, [azidobenzoyl-D- Lys6 ]-GnRH. Both analogs bind with high affinity to a single class of receptors, with apparent IC50 values of 0.5 nM and 1 nM, respectively. The binding of 125I-labeled Buserelin to pituitary membranes was inhibited, in a dose-responsive manner, by both trypsin and chymotrypsin, with the former being less effective. Neuraminidase at a concentration up to 100 micrograms/ml did not affect the binding. Lectins, such as concanavalin A and wheat-germ agglutinin, at a concentration range of 20-200 micrograms/ml had no effect on the binding, whereas soybean agglutinin at high concentrations (150 and 200 micrograms/ml) slightly inhibited the specific binding. Photoaffinity labeling of the bovine pituitary GnRH receptors resulted in the identification of two specific bands with apparent molecular weights of 60 K and 30 K daltons. The latter probably represents very low affinity binding sites. Both specific bands were sensitive to trypsin and chymotrypsin treatment but were not affected by neuraminidase treatment. These results suggest a slight difference between rat and bovine pituitary GnRH receptors.
mesh_terms: D000818:Animals; D001386:Azides / Q000378:metabolism; D001667:Binding, Competitive; D002064:Buserelin / Q000378:metabolism; D002417:Cattle; D002918:Chymotrypsin / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives / Q000378:metabolism; D037102:Lectins / Q000494:pharmacology; D008566:Membranes / Q000378:metabolism; D008970:Molecular Weight; D009439:Neuraminidase / Q000378:metabolism; D010902:Pituitary Gland / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000378:metabolism*; D011966:Receptors, LHRH; D014357:Trypsin / Q000378:metabolism
chemical_list: D001386:Azides; D037102:Lectins; D011956:Receptors, Cell Surface; D011966:Receptors, LHRH; D007987:Gonadotropin-Releasing Hormone; C031737:LHRH, N-epsilon-azidobenzoyl-Lys(6)-; D009439:Neuraminidase; D002918:Chymotrypsin; D014357:Trypsin; D002064:Buserelin