T-kinin is resistant to hydrolysis by angiotensin I-converting enzyme

Several enzymes of are capable of cleaving kinins at either the N- or C-terminal end. In this work, we investigated the hydrolysis of T-kinin (TK) and bradykinin (BK) by carboxypeptidase B (CpB) and angiotensin I-converting enzyme (ACE). The kinins were incubated with the enzymes in Tyrode solution kept at 37 degrees C for 25 min. The kinin residual activity in the incubation medium was bioassayed on the isolated guinea pig ileum. BK (5 micrograms/ml) and TK (5 micrograms/ml) were rapidly and similarly degraded by CpB (0.088 mU/ml) since half of both kinins was inactivated within 5 min of incubation. At 25 min of incubation with CpB the TK and BK-like activities were 20.8 +/- 3.9 (1.04 +/- 0.20 micrograms/ml) and 31.8 +/- 5.0% (1.59 +/- 0.25 micrograms/ml) of the initial kinin concentrations, respectively. BK was also rapidly inactivated by ACE (5 mU/ml) while TK activity was unaffected. At 25 min the BK and TK residual activities corresponded to 39.4 +/- 2.5 (1.97 +/- 0.13 micrograms/ml) and 93.8 +/- 9.2% (4.69 +/- 0.46 micrograms/ml) of the initial kinin concentrations, respectively. It was concluded that TK, a kinin elongated at the N-terminal position, is resistant to ACE degradation.