Synthesis and characterization of 2-nitro-5-aziodobenzoylglycyloxytocin, an oxytocin photoaffinity label.

The oxytocin analogue, 2-nitro-5-azidobenzoylglycyloxytocin (NAB-Gly-oxytocin), has been synthesized and purified. The analogue is a full agonist for the stimulation of osmotic water flow in the toad urinary bladder (one-half maximal activity at 3.2 X 10(-6)M). It also enhances [14C]urea permeability in this tissue. Repetitive photolysis in the presence of NAB-Gly-oxytocin (8 X 10(-6)M) results in a progressive permanent inhibition of oxytocin stimulated urea permeability but does not alter hormone induced 3H2O movement. The inhibition is dependent on the photogeneration of the aryl nitrene intermediate and is relieved by protecting the hormone receptor with excess oxytocin (10(-6)M) during the photolysis. These results suggest that the photodependent permanent inhibition of the response to oxytocin in the toad bladder is due to covalent incorporation of the photoaffinity label, NAB-Gly-oxytocin, into the hormone receptor.