Active kallikrein, preprokallikrein, and kallikrein-inhibitor complex

Active kallikreins isolated from various exocrine and endocrine tissues were identified by a monoclonal antibody in Western blot analyses to be approximately 38,000 dalton proteins. Kallikreins isolated from rat pancreas, kidney, submandibular gland, brain, spleen and urine were indistinguishable with respect to molecular weight and immunological characteristics. Preprokallikreins were synthesized in a cell-free translation system directed by mRNAs and immunoprecipitated by affinity-purified kallikrein antibody. Analysis of the precipitates by SDS-polyacrylamide gel electrophoresis revealed a approximately 37,000 dalton polypeptide in kidney, brain and submandibular gland translation products. This 37,000 dalton kallikrein precursor was hybrid-arrested by a kallikrein cDNA encoding tissue kallikrein which was isolated from a rat submandibular gland cDNA library. The immunoprecipitates of products directed by pancreatic mRNA showed a major protein with Mr of approximately 30,000. An endogenous approximately 92,000 dalton component in rat urine and kidney was also identified by a monoclonal antibody to tissue kallikrein and represents a kallikrein-inhibitor complex. These results indicate that tissue kallikreins can be initially synthesized as 37,000 or 30,000 dalton prepropeptides and then converted into a 38,000 dalton active form by proteolytic processing and glycosylation. The active kallikrein is capable of binding to an inhibitor to form a 92,000 dalton complex.