Hydrolysis of Bradykinin by Angiotensin-Converting Enzyme

Abstract

Two dipeptides, phenylalanylarginine (Phe-Arg) and serylproline (Ser-Pro), are released sequentially from bradykinin by angiotensin-converting enzyme purified from hog lungs; chloride increases the rate of release of both dipeptides. Using an automated ninhydrin-reagent method, we studied the kinetics of bradykinin hydrolysis. The reaction proceeded in the absence of chloride; however, the addition of chloride increased the rate of hydrolysis by decreasing K m and increasing V m . The K m values for bradykinin were 3.9 x 10~6M in the absence of chloride and 0.85 x 10~6M in the presence of 0.01M NaCl (optimal concentration). Both of these K m values were well below the value of 30 x 10" 6 M determined for angiotensin I at its optimal chloride concentration of 0.1M. Hydrolysis of bradykinin had a pH optimum of 7 and was inhibited by low concentrations (10~6M) of ethylenediaminetetraacetic acid or the nonapeptide pyroglutamyl (Pyr)-Trp-Pro-Arg-Pro-Gln-Ile-Pro-Pro. It is concluded that one enzyme, acting as a dipeptidyl carboxypeptidase, catalyzes both the conversion of angiotensin I to angiotensin II and the hydrolysis of bradykinin. KEY WORDSphenylalanylarginine enzyme kinetics dipeptidyl carboxypeptidase chloride activation serylproline hog lung Bothrops jararaca nonapeptide

Kallidin- and Bradykinin-Degrading Pathways in Human Heart

“…Indeed, in vitro experiments have demonstrated that purified ACE readily degraded BK to BK-(1-7), 5 and, in in vivo experiments, the use of ACE inhibitors increased the blood levels of BK in rats, suggesting that degradation of BK by ACE was reduced. 6 Our results, in contrast, suggest that ACE plays only a minor role in the metabolism of kinins in the membrane fraction of heart tissue.…”

“…Indeed, in vitro experiments have demonstrated that purified ACE readily degrades BK to BK-(1-7) and further to BK-(1-5). 5 Moreover, inhibition of ACE has been shown to increase the blood levels of BK in rats 6 and the outflow of BK from isolated perfused rat hearts. 7 However, recent findings have suggested that part of the beneficial effects of ACE inhibitors can be attributed to their direct effects on bradykinin receptors rather than to their inhibitory effect on the degradation of kinins.…”

Angiotensin-converting enzyme in cultured endothelial cells. Synthesis, degradation, and transfer to culture medium.

“…We find that the radiolabel disappears from the cellular enzyme in two kinetic components, one of which corresponds to the release of enzyme to the medium. Finally, we find that the incorporation of 3 H-leucine into new enzyme is higher when cells are maintained in medium containing serum than when they are maintained in serum-free medium.…”

“…The cell-associated form behaves on lectin affinity columns like purified enzyme from kidney, and the soluble, released form, like enzyme from plasma. 8 We present here a study of the incorporation of 3 Hleucine into angiotensin-converting enzyme, and the rates of degradation and release of enzyme in cultured arterial endothelial cells from swine. The data are consistent with the hypothesis that the medium enzyme is shed from the cell surface.…”

Effect of intraperitoneally administered hydrolyzed whey protein on blood pressure and renal sodium handling in awake spontaneously hypertensive rats

“…Peptides with hypotensive activity have been identified in hydrolysates of gelatin, casein, maize endosperm protein, and fish muscle (6)(7)(8)(9), and are believed to be useful as functional dietary ingredients for hypertensive patients. This activity is attributable mainly to the inhibition of angiotensin-I-converting enzyme (ACE), which plays a prominent role in the regulation of arterial blood pressure by converting the inactive decapeptide angiotensin I to a strong vasoconstrictor octapeptide, angiotensin II, while at the same time inactivating the vasodilator and natriuretic nonapeptide, bradykinin (10,11).…”