Acid-activatable inactive renin in cat plasma and kidney.

Inactive renin has been identified in cat plasma and kidney extracts. It is identical to human plasma prorenin in all respects tested except that the pH optimum of activated cat inactive renin is slightly different from that of active renin. To further investigate whether cat inactive renin is indeed prorenin we examined whether it could be reversibly acid-activated, an unusual characteristic of human prorenin. We found that dialysis of partially purified, cat renal inactive renin to pH 3.3 caused reversible acid activation. In plasma, when acidification was followed by a second dialysis to pH 7.4 at 4 degrees C, irreversible activation took place, just like human prorenin. Unlike human angiotensinogen, cat angiotensinogen was apparently not affected by acid dialysis. These results suggest that cat inactive renin is most likely prorenin.