Kinetic studies of rat renin and tonin on purified rat angiotensinogen

Kinetic studies of highly purified rat renin and rat tonin on completely purified angiotensinogen and angiotensin-tetradecapeptide synthetic renin substrate were performed. The Michaelis-Menten constant (Km) for renin, determined at the optimum pH, was 2.8 +/- 0.03 microM for angiotensinogen and 28.8 +/- 2.69 microM for angiotensin-tetradecapeptide renin substrate. The Km of purified rat tonin was determined as 0.66 +/- 0.18 microM for angiotensinogen and 2.33 +/- 0.42 microM for angiotensin tetradecapeptide. In comparison with renin, tonin shows higher affinity with respect to angiotensinogen, but the turnover number of natural substrate molecules observed with renin (0.87 s-1) is more than 3700 times higher than that of tonin (2.3 X 10(-4) s-1). Renin shows higher affinity to angiotensin tetradecapeptide than tonin, but similar turnover numbers of 2.8 and 10.0 s-1 are observed for hydrolysis of angiotensin tetradecapeptide by renin and tonin, respectively.