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. 2021 May;72(2):529-538.
doi: 10.1007/s12020-020-02572-2. Epub 2021 Jan 7.

125I-Angiotensin 1-7 binds to a different site than angiotensin 1-7 in tissue membrane preparations

Filipe F Stoyell-Conti  1   2 , Sarin Itty  3   4 , Christy Abraham  3   4 , Katya Rigatto  5   6 , Crystal A West  7 , Robert C Speth  8   9
Affiliations

125I-Angiotensin 1-7 binds to a different site than angiotensin 1-7 in tissue membrane preparations

Filipe F Stoyell-Conti et al. Endocrine. 2021 May.

Abstract

Purpose: To study the receptor for Angiotensin (Ang) 1-7 using a radioligand (125I-Ang 1-7)-binding assay. For more than a decade, Mas has been viewed as the receptor for Ang 1-7; however, Ang 1-7 binding has not been pharmacologically characterized in tissue membrane preparations.

Methods: Radioligand-binding assays were carried out using tissue membrane preparations using radioiodinated Angiotensin 1-7 (125I-Ang 1-7) to characterize its binding site. Non-radioactive 127I-Ang 1-7 was used to test if the addition of an iodine to the tyrosine4 moiety of Ang 1-7 changes the ability of Ang 1-7 to competitively inhibit 125I-Ang 1-7 binding.

Results: 125I-Ang 1-7 binds saturably, with moderately high affinity (10-20 nM) to a binding site in rat liver membranes that is displaceable by 127I-Ang 1-7 at nanomolar concentrations (IC50 = 62 nM) while Ang 1-7 displaces at micromolar concentrations (IC50 = 80 µM) at ~22 °C. This binding was also displaceable by inhibitors of metalloproteases at room temperature. This suggests that 125I-Ang 1-7 binds to MMPs and/or ADAMs as well as other liver membrane elements at ~ 22 °C. However, when 125I-Ang 1-7-binding assays were run at 0-4 °C, the same MMP inhibitors did not effectively compete for 125I-Ang 1-7.

Conclusions: The addition of an iodine molecule to the tyrosine in position 4 of Ang 1-7 drastically changes the binding characteristics of this peptide making it unsuitable for characterization of Ang 1-7 receptors.

Keywords: Angiotensin 1–7; Iodoangiotensin 1–7; Metallopeptidases; Radioligand-binding assay.

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