Effects of carbohydrate removal on the structure and activity of bovine lutropin

Bovine lutropin was successfully deglycosylated by treatment with anhydrous HF at 0 degrees C for 60 min. The overall loss of carbohydrate residues was about 70%. Fucose, mannose and galactosamine residues were removed completely. About six residues of N-acetylglucosamine were left in the deglycosylated hormone. This degree of deglycosylation did not reduce receptor binding ability but in vitro biological activity was completely lost. Consistent with these properties, the deglycosylated lutropin inhibited the in vitro biological action of the native lutropin. The results demonstrate that the full complement of carbohydrate residues including the sulfated hexosamines are not required for receptor binding but they are necessary to impart appropriate conformational features necessary for activation of the target cells.