A Plasma Serine Protease would be Responsible of Inactive Renin Processing in Kidney

pp 761-768

Abstract

The aim of the present research was to characterize a plasma protein fraction (PreR-Co) involved in renin activation. The PreR-Co was obtained as a single electrophoretic band from rat plasma by(NH4)2SO4precipitation, Sephacryl S-200 HR, immunoafinity with an anti-rat albumin and ion-exchange chromatography. The N-terminal aminoacid sequence was studied, as well as amidase, esterase and kallikrein activities. Rat kidney extract (KE)or plasma were incubated with purifiedPreR-Co during 15 minutes at 37°C and renin concentration was measured by incubation with homologous angiotensinogen. Plasma or KE were also activated by trypsin.

Results

The purified enzyme has a molecular weight of 37kDa and N-terminal amino acid sequence was IIGGSMDAKGSFP, which has 90% homology to the R-chain of haptoglobin, 69% to serine-proteases and 65% to kallikreins. There was a six-fold in-crease in renin concentration when KE was incubated with purified PreR-Co while renin activity increased 4 times when KE was treated with trypsin.The enzyme activity was inhibited by DFP, PMSF and aprotinin. PreR-Co was unable to process inactive plasma renin (prorenin) even after addition of up to 50.tg of enzyme (67.6± 13.3 and 73.7 ±11.1ng Ang I/ml/h).

Conclusions

These results suggest thatPreR-Co could be a serine protease carried to the kidney by albumin where PreR-Co processes inactive renal renin. Consequently, this protease may play an important role in the balance of circulating renin.