A renin inhibitor from rabbit kidney: conversion of a large inactive renin to a smaller active enzyme

Renin in extracts of frozen rabbit kidney exists in two forms: active (molecular weight about 37,000) and inactive (molecular weight about 55,000) renin. The inactive form becomes active after exposure to pH 2.5 at 4 degrees C. If extracts are chromatographed on DEAE cellulose, the inactive renin dissociates into active renin plus a renin inhibitor (molecular weight about 13,000). The inhibitor recombines with active renin if the two are incubated together at 37 degrees C. The inhibitor is destroyed by acid treatment at pH 2.5 at 4 degrees C. We conclude that the activation of inactive renin is due to destruction of the inhibitor by acid. The inactive material may be a renin proenzyme or a storage form of active renin combined with inhibitor.