Photoaffinity labeling of the antidiuretic hormone receptor.

A study to determine the feasibility of photoaffinity labeling the antidiuretic hormone receptor in the toad urinary bladder has been carried out. Two photoactivated derivatives of oxytocin have been synthesized, purified, and characterized chemically and biologically. Photolysis of the toad bladder in the presence of one of these derivatives, 2-nitro-5-azidobenzoylglycyloxytocin, produces a permanent inhibition of the response to native oxytocin. This inhibition can be relieved by protecting the hormone receptor with excess oxytocin during the photolysis. These results suggest that the photolysis-dependent inhibition of the response to native hormone is due to covalent incorporation of the photoaffinity label into the hormone receptor.