Subcellular Localization in Rat Brain of Angiotensin-Related Carboxypeptidase Activity Distinct from Converting Enzyme

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Abstract
Whole brain synaptosomes contain both an isorenin activity and angiotensin-related carboxypeptidase activity. Further hydrolysis of des-Leu angiotensin I (AI-dL) occurs more slowly; hydrolysis of angiotensin II (AII) is negligible. Vasopressin and oxytocin but not vasotocin can inhibit angiotensin-related carboxypeptidase activity. Since AII has been shown to induce vasopressin secretion, this correlation suggests a feedback inhibition by vasopressin of this enzymatic cascade. Commercially available radioimmunoassays for AI and AII show a 3.4 and 6.0% crossreactivity, respectively. When the absolute concentration of AI-dL exceeded 500 ng/ml, both antibodies to AI and AII showed maximal displacement of radiolabel. This suggests that these antibodies may not distinguish between AI-dL from other peptides during immunocytochemistry.

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