Analysis of the adrenal angiotensin II receptor with the photoaffinity labeling method

The angiotensin II (Asp-Arg-Val-Tyr-Ile-His-Pro-Phe, AT) receptor of bovine adrenocortex has been investigated with photosensitive analogues of AT. In a first series of experiments, we have shown that isolated cortical cells secrete aldosterone in a permanent and specific manner if they have been photolyzed in the presence of the photolabel [Sar1,(4'-N3)Phe8]AT. This permanent stimulation is in contrast to the smooth muscle assays where under similar conditions a permanent and specific block was always observed. It is assumed that the irreversible occupation of the AT receptor produces this effect. In a second type of experiment, we have shown that the AT binding site on adrenocortical membranes can be specifically and irreversibly occupied under similar conditions and that this occupation can be prevented in a competitive manner by the presence of nonphotosensitive hormone. Using a radioactive label, [Sar1,(3'-125I)Tyr4,(4'-N3)Phe8]AT, we have identified the AT receptor as a 300-kDa protein by means of gel filtration under nonreducing and nondenaturating conditions. Under reducing and denaturing conditions, a subunit of 60 kDs was found by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and gel filtration. The AT receptor is proposed to be a 300-kDa protein with one binding subunit of 60 kDa.