Two-step prorenin-renin conversion. Isolation of an intermediary form of activated prorenin.

F.H Derkx,M.P Schalekamp,M.A Schalekamp

doi:10.1016/s0021-9258(18)61528-5

Abstract

Prorenin is an inactive form of the aspartic protease renin. Like pepsinogen, it is activated at low pH. The kinetics of acid activation of prorenin were studied in human amniotic fluid and plasma and in preparations of purified prorenin isolated from amniotic fluid and plasma. Conversion of prorenin (pR) into active renin (R) appeared to be a two-step process involving the generation of an intermediary form of activated prorenin (pRa). The pR----pRa step is an acid-induced reversible change in the conformation of the molecule, and the pRa----R step is proteolytic. pRa----R conversion occurred in amniotic fluid at low pH by the action of an endogenous aspartic protease. In plasma pRa----R conversion occurs after restoration of pH to neutral and is caused by the serine protease plasma kallikrein. pRa----R conversion did not occur in purified preparations of prorenin. Thus, in contrast to pepsinogen, the acid-induced reversible conformational change is not followed by autocatalysis. pRa of amniotic fluid and plasma could be separated from R by affinity chromatography on Cibacron blue F3GA-agarose, and R but not pRa was detected by an immunoassay using monoclonal antibodies reacting with R and not with pR. The first-order rate constant for pR----pRa conversion depends on the protonation of a polar group (or groups) with pK approximately 3.4, the rate constant being proportional to the fraction of pR molecules that have this group protonated. This is analogous to the reversible acid-induced conformational change of pepsinogen that occurs before its proteolytic conversion into pepsin. kcat/Km for pRa----R conversion by plasmin and plasma kallikrein at pH 7.4 and 37 degrees C was 7.8 X 10(6) and 5.2 X 10(6) M-1 min-1, respectively, which was about 50-70 times greater than for pR----R conversion. The susceptibility of pRa to proteolytic attack is high enough for the intrinsic factor XII-kallikrein pathway to cause rapid pRa----R conversion at 37 degrees C even in whole blood with its abundance of serine protease inhibitors. Formation of pRa may occur in vivo in an acidic cellular compartment, such as exo- or endocytotic vesicles.

Highlights

Prorenin is an inactive formof the aspartic protease after the pH hasbeen brought back to neutral
The involves the inactivation of one or more protease inhibitors kinetics of acid activationof prorenin were studied in at low pH, followed by activation of prekallikrein by factor human amniotic fluid and plasma and in preparations XI1 and conversion of prorenin into renin at neutral p H by of purified prorenin isolated from amniotic fluid and the action of kallikrein itself or by other proteases activated plasma
PRa + R conversion occurred in amniotic fluid at low pH by the action of a n endogenous aspartic proclearly demonstrated by the enhanced spontaneous proreninrenin conversion at 4 “C in plasma from which C1-esterase inhibitor, a2-macroglobulin, and antithrombin I11 had been selectively removed by immunoadsorption [4]

Summary

Introduction

Prorenin is an inactive formof the aspartic protease after the pH hasbeen brought back to neutral. The involves the inactivation of one or more protease inhibitors kinetics of acid activationof prorenin were studied in at low pH, followed by activation of prekallikrein by factor human amniotic fluid and plasma and in preparations XI1 and conversion of prorenin into renin at neutral p H by of purified prorenin isolated from amniotic fluid and the action of kallikrein itself or by other proteases activated plasma. The importance of inactivation of serine (R) appeared to be a two-step process involving the protease inhibitors for subsequent activationof prorenin was generation of an intermediary formof activated prorenin (pRa). Sion at neutral pH after exposure of plasma to low pH, the in contrast to pepsinogen, the acid-induced reversible activation of prorenin during exposure to low pH appears to conformationalchange is not followed by autocata- involve a reversible process, since the activated prorenin is lysis. The first-orderrate constant prorenin molecule causes it to become moresusceptible to

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Conclusion