Reversal of the antagonism of deglycosylated human chorionic gonadotropin by aggregation with wheat germ agglutinin.
Human chorionic gonadotropin (hCG) behaves as an antagonist upon chemical deglycosylation with hydrogen fluoride. In this study it was found that the alpha- and beta-subunits of deglycosylated hCG (DGhCG) still retained their ability to bind to wheat germ agglutinin (WGA) but not to concanavalin A. The antagonism of DGhCG against activation of adenylate cyclase and steroidogenesis was reversed, when WGA was bound to the N-linked carbohydrate moieties of hCG alpha- and beta-subunits followed by addition of purified Leydig cells. The complex formed by incubation at an approximately equimolar ratio induced the maximal reversal of antagonism. This reversal of antagonism was diminished by addition of N-acetylglucosamine. No increase of steric hindrance at the receptor sites was seen in binding studies of the [125I]DGhCG-WGA complex, indicating that the receptor-binding domain of hCG may not be adjacent to the carbohydrate moieties. Kinetic studies of the hormonal response showed that the DGhCG-WGA complex terminated cAMP accumulation after 30 min of incubation, but not testosterone production. Our results suggest that tetravalent WGA can also reverse the antagonism of DGhCG, as in bivalent antibodies to hCG beta.
Hattori
M
M
Department of Pharmaceutical Chemistry, Gunma University, Maebashi, Japan.
Shimohigashi
Y
Y
Wakabayashi
K
K
D006063:Chorionic Gonadotropin / Q000378:metabolism / Q000494:pharmacology*; D003208:Concanavalin A / Q000378:metabolism; D000242:Cyclic AMP / Q000096:biosynthesis; D006858:Hydrofluoric Acid; D066298:In Vitro Techniques; D007700:Kinetics; D007985:Leydig Cells / Q000378:metabolism; D008297:Male; D009005:Monosaccharides / Q000494:pharmacology; D013739:Testosterone / Q000096:biosynthesis; D014909:Wheat Germ Agglutinins / Q000378:metabolism*
D006063:Chorionic Gonadotropin; C034923:HCG, deglycosylated; D009005:Monosaccharides; D014909:Wheat Germ Agglutinins; D003208:Concanavalin A; D013739:Testosterone; D000242:Cyclic AMP; D006858:Hydrofluoric Acid