Activities of deglycosylated thyrotropin at the thyroid membrane receptor-adenylate cyclase system

Abstract

A bovine thyrotropin (bTSH) preparation was deglycosylated by treatment with anhydrous hydrogen fluoride (HF) in the presence of anisole. The resulting material consisted of TSH derivatives that exhibited different molecular sizes, all smaller than the native hormone. The majority (62%) of the deglycosylated TSH derivatives did not bind to the lectin concanavalin A, while 98% of the native TSH was able to bind. The deglycosylated TSH derivatives bound to the high affinity-high specificity TSH binding sites in human thyroid membranes with a potency more than twice that of equivalent immunological amounts of the native bTSH. Despite the enhanced binding affinity for the TSH receptor, the deglycosylated TSH derivatives were unable to stimulate adenylate cyclase fully. Maximal stimulation achieved with bTSH derivatives was only 9 to 17% of the’maximal stimulation achieved with native bTSH. Further, the deglycosylated derivatives competitively inhibited stimulation of the thyroidal adenylate cyclase by native bTSH. We conclude that HF treatment of bTSH results in partially deglycosylated TSH derivatives that exhibit enhanced ability to bind to the TSH receptor and markedly diminished adenylate cyclase-stimulating activity.