Angiotensin II Inactivation Process in Cultured Mouse Spinal Cord Cells

The pattern of hydrolysis of [3H]angiotensin II ( [3H]AII; 20 nM) by intact cells was studied on cultured mouse spinal cord cells. Degradation products were identified by HPLC analysis after incubation for 2 h at 37 degrees C. In the absence of peptidase inhibitors, 70% of [3H]AII was degraded, and the main labeled metabolite was [3H]tyrosine (40% of total radioactivity). Minor quantities of [3H]AII1-5 and [3H]AII4-8 were formed. Results obtained in the presence of various inhibitors indicate that several enzymes were involved in the AII-hydrolyzing process. Dipeptidyl aminopeptidase III (EC 3.4.14.4) could play a critical role, as suggested by the formation of [3H]Val3-Tyr4 and [3H]-Tyr4-Ile5 in the presence of bestatin (2 X 10(-5) M). This hypothesis was confirmed by the potency of dipeptidyl amino-peptidase III inhibitors to inhibit both [3H]AII hydrolysis and formation of these 3H-labeled dipeptides. An arylamidase-like activity could also be participating in [3H]AII hydrolysis, because higher concentrations of bestatin (10(-4) M) in association with dipeptidyl aminopeptidase III inhibitors totally inhibited [3H]tyrosine formation, increased protection of [3H]AII and [3H]AII1-7 formed, and provoked a slight accumulation of [3H]AII2-8. These results suggest that the formation of [3H]AII2-8 is due to the action of a bestatin-insensitive acidic aminopeptidase and that the Pro7-Phe8 cleavage is also a step of AII hydrolysis, resulting from the action of an unidentified peptidase different from prolyl endopeptidase.(ABSTRACT TRUNCATED AT 250 WORDS)