Photochemical inactivation of the angiotensin receptor of rabbit aorta by N.alpha.-(2-Nitro-5-azidobenzoyl)-[1-aspartic acid,5-isoleucine]angiotensin II

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Abstract
The photoaffinity label N.alpha.-(2-nitro-5-azidobenzoyl)-[Asp1,Ile5]angiotensin[A]II (nitroazidobenzoyl-AII) has a pD2 of 7.22 in the rabbit aortic strip assay compared to 8.44 for [Asp1,Ile5]AII and can be completely inhibited by [Sar1,Ala8]AII. Photolysis of a single dose of nitroazidobenzoyl-AII (0.1 .mu.M) with aortic strips for 3 min with light of wavelengths > 320 nm, followed by washing, resulted in loss of .apprx. 25% of the strip''s response to a subsequent dose of nitroazidobenzoyl-AII. Photolysis of 3 consecutive doses of label resulted in loss of 62% of the strips response to a subsequent dose. Repetitive exposure to label in the dark and repetitive photolyses without label resulted in loss of not > 20% of the strips ability to respond to AII. Photolysis with 3 consecutive doses of 0.1 .mu.M nitroazidobenzoyl-AII in the presence of 0.5 .mu.M of the competitive inhibitor [Sar1,Ala8]AII decreased the observed inhibition from 62 to 22%. The long-lasting inhibition observed after photolysis with 0.1 .mu.M nitroazidobenzoyl-AII occurred via photolysis of some part of the nitroazidobenzoyl chromophore. This inhibition was mediated via the receptor that binds [Sar1,Ala8]AII and, therefore, AII.