The effect of sialic acid on adenylate cyclase activity and thyrotropin-receptor binding in human thyroid membranes.

Exogenous sialic acid at 3 mM and higher concentrations inhibits the basal adenylate cyclase activity and the activity stimulated by thyrotropin (TSH) and fluoride in the human thyroid membrane fraction; 30 mM-sialic acid acts as an inhibitor of TSH binding. The decrease of these activities at high sialic acid concentrations might be ascribed to changes in membrane conformation caused by acidic character of this sugar.