Untersuchungen �ber die Serum-Angiotensinase

Aminopeptidase A is angiotensinase A. II. Biochemical studies on aminopeptidase A and M in rat kidney homogenate

Biochemical fluorometric methods were used to investigate aminopeptidase A (APA; E.C.3.4.11.7) in the rat kidney homogenate and glomeruli and to compare it with aminopeptidase M (APM; E.C.3.4.11.2). It is shown that APA is a calcium-ion-dependent enzyme, while APM is not. To clarify the functional importance of APA and APM in the kidney, their activities were measured under the influence of angiotensins. Fluorimetric measurements in renal homogenate (with 2-naphthylamide derivatives as substrates), which represents mixed-enzyme tissue preparations containing a variety of peptidases besides APA and APM, showed a Km of 0.13 mM for APA and competitive inhibition of ANG II (K1 = 0.015 mM), and a Km of 0.24 for APM and competitive inhibition by ANG III (K1 = 0.003 mM). The remaining two angiotensins showed non-competitive inhibition of APA (ANG I, III) and APM (ANG I, II) in this preparation. For comparison purposes, fluorometric measurements were performed in microdissected glomeruli which contain only APA. A Km of 0.23 mM for the APA and a competitive inhibition of APA by ANG I and II were determined. Thus it was possible to show biochemically that APA is equivalent to angiotensinase A and that both APA and APM participate in angiotensin degradation in the kidney. APA initiating the breakdown of ANG I and II, and APM possibly continuing it in sequential fashion.

Total immunoreactive angiotensin ii, its hepta-octapeptide fraction, and its hexapeptide in patients with liver disease

Arterial and venous plasma concentrations of total immunoreactive angiotensin II (AT II), its bioactive hepta-octapeptide fraction and its inactive hexapeptide were measured in normal subjects (n=16), in patients with acute viral hepatitis (n=12), and in treated (n=16) and untreated (n=17) patients with cirrhosis of the liver and ascites. Independent of normal or increased values of total immunoreactive AT II, the ratio between the hepta-octapeptides and the hexapeptide remained unchanged. This might indicate continuous octapeptide generation and balanced metabolite turnover throughout the systemic circulation. Moreover, a significant arterio-venous peptide gradient was lacking. It has to be concluded that total venous plasma AT II sufficiently reflects both the arterial hormone concentration and its major fraction of hepta-octapeptides in arterial (79%) and venous (76%) blood.