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

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Abstract
The angiotensin II (Asp-Arg-Val-Tyr-Ile-His-Pro-Phe, AT) receptor of bovine adrenocortex was investigated with photosensitive analogs of AT. In a first series of experiments, 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 2nd type of experiment, the AT binding site on adrenocortical membranes can be specifically and irreversibly occupied under similar conditions and 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, the AT receptor was identified as a 300-kDa [dalton] protein by means of gel filtration under nonreducing and nondenaturating conditions. Under reducing and denaturating conditions, a subunit of 60 kDa was found by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and gel filtration. The AT receptor is proposed to be a 300-kDa protein with 1 binding subunit of 60 kDa.

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