Studies on Pituitary Follitropin. X. Biochemical, Receptor Binding and Immunological Properties of Deglycosylated Ovine Hormone

Treatment of ovine pituitary follitropin with anhydrous hydrogen fluoride at 0 degrees C for 60 min resulted in the removal of approximately 80% of the sugars without affecting the polypeptide moiety. Fucose, sialic acid and N-acetylgalactosamine were eliminated completely while the loss of hexoses and N-acetylglucosamine amounted to 86% and 56% respectively. The treatment had no effect on the quaternary structure of the hormone. Consistent with the loss of carbohydrate, the elution volume of the hormone on Sephadex G100 was increased and the deglycosylated hormone lost its ability to interact with the lectin concanavalin-A immobilized on Sepharose. Deglycosylation rendered the hormone less acidic as reflected by altered electrophoretic mobility in polyacrylamide gels at pH 8.9 and 4.5. The UV absorption spectrum of the hormone was not affected by deglycosylation but tryptophan fluorescence was slightly decreased. The receptor-binding activity of the hormone as estimated by a specific radioreceptor assay using adult bovine testicular membranes and labeled 125I-FSH was increased by 250% following deglycosylation. In a conformation specific radioimmunoassay, the deglycosylated hormone showed 150% activity as compared to the native hormone. Thus, the full integrity of the carbohydrate moiety in ovine follitropin is not required for effective receptor binding and immunological activity.