Angiotensin Converting Enzyme A Peptidyl Dipeptide Hydrolase

Metabolism of angiotensinogen by renin produces the decapeptide angiotensin I. This relatively inactive pep-tide is acted on by a dipeptidase-converting enzyme to produce the very active octapeptide angiotensin II. In addition to converting enzyme, angiotensin I can be acted on by prolyl endopeptidase, an enzyme that removes the first amino acid to form angiotensin 1-7, a peptide primarily active in the brain. ACE has been identified in vascular endothelial cells, epithelial cells of the proximal tubule and small intestine, male germinal cells, and the central nervous system. The lung vascular endothelium contains the highest concentration of ACE, and therefore, the lung serves as the major organ for the production of circulating angiotensin II. Although ACE was originally thought to be specific for the conversion of angiotensin I to II, it is now known to be a rather nonspecific peptidyl dipeptide hydrolase that can cleave dipeptides from the carboxy terminus of a number of endogenous peptides (e.g., substance P, bradykinin). Peptides with penultimate prolyl residues are not cleaved by converting enzyme; this accounts for the biological stability of angiotensin II. Inhibition of converting enzyme results in an elevated pool of an-giotensin I. A mutation deletion in the ACE gene has been linked to a higher risk factor for hypertension, left ventricular hypertrophy, and myocardial infarction.

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