Kallikrein isolated from commercial crystalline pepsin preparations.

1. An experiment designed to study the relationship between pH and kininogenase activity of three commercial preparations of porcine crystallized pepsin showed that each preparation had two well separated pH optima, pH 4 and 8. 2. From the inhibition spectrum of the pH 8 kininogenase it was concluded that it is a kallikrein of the glandular type, since it proved to be a serine protease and was insensitive to protein trypsin inhibitors. 3. Kallikrein activity can be separated from pepsin by affinity chromatography on Sepharose-4B-Pro-Phe-agmatine. This separation permitted us to obtain purified material with kallikrein specific activity 43 times higher than that of crude pepsin and which showed a single band on polyacrylamide gel electrophoresis. 4. The kallikrein activity was found to have a molecular weight of 36 kDal and a Michaelis constant of 25 microM when acting on Bz-Pro-Phe-Arg-p-nitroanilide at pH 8.6. 5. On the basis of these properties, kallikrein from commercial pepsin resembles the kallikreins previously described from rat or human stomach.