Blocking of catecholamine activation of adenylate cyclase by N, N'dicyclohexyl carbodiimide in turkey erythrocytes

Abstract

Incubation of erythrocytes or their isolated membranes with N, N'dicyclohexyl carbodiimide (DCC) blocked isoproterenol activation of the adenylate cyclase. Fluoride activation remained unaffected. L-epinephrine and DL-propranolol partially and transiently protected the system against DCC. D-Epinephrine and dopamine did not protect. The enzyme system preactivated by isoproterenol plus Gpp(NH)p was no longer sensitive to DCC. In contrast to the water insoluble DCC, a water soluble carbodiimide acted only at high concentration and blocked fluoride as well as catecholamine activation of the adenylate cyclase. The findings indicate that DCC attacks a group on, or near, the beta-adrenergic receptor and that this group is located in a hydrophobic region of the cell membrane. It is argued that a low nominal concentration of DCC in the aqueous suspension of erythrocytes actually represents a very high concentration of DCC in the hydrophobic region of the cell membranes, near the beta-adrenergic receptor. The reaction with DCC may prove to be a useful tool in future analyses of beta-adrenergic receptor function.