Purification and partial characterization of a thiol proteinase activating prokallikrein from the rat kidney cortex

The rat kidney cortex contains at least three kinds of prokallikrein-activating proteinase, and among these the one with the highest molecular weight was purified by a procedure including chromatography on CM-cellulose, concanavalin A-Sepharose, organomercurial-Sepharose 4B and Sephadex G-100. The resulting preparation was apparently homogeneous, as assessed by SDS-polyacrylamide gel electrophoresis. The molecular weight was estimated to be 57,000. The optimal pH for the activation of prokallikrein by the preparation, termed activator I, was around 4.5. Activator I was inhibited by E-64, iodoacetate and leupeptin, but not by PMSF and phosphoramidon. In immunodiffusion analysis, the antiserum to activator I formed an immunoprecipitin arc with the extract from the kidney cortex or submandibular gland, but not with that from the pancreas. These results indicate that activator I is a thiol proteinase with a molecular weight of 57,000. A proteinase immunologically identical with activator I appears to be present in the submandibular gland.