Kinin-forming enzymes in vascular tissue.

The present study was undertaken to examine whether there is a kallikrein-like enzyme in vascular tissue. Isolated saline-perfused rat mesenteric arteries were used. A kallikrein-like enzyme and acid protease from saline-perfused mesenteric arteries were separated by CM-cellulose chromatography with a linear NaCl gradient. The separation made it possible to study the optimum pH of the kallikrein-like enzyme and acid protease. The kallikrein-like enzyme showed optimal activity in the range of pH 7-9 and the acid protease in the range of pH 4-5. Both enzymes when acting on a protein plasma substrate release an active peptide that has a similar chemical and pharmacological properties to bradykinin. Using antibodies that specifically inhibit kinins, the biological action was completely abolished. These results indicate that arterial tissue contains two enzymes which generate kinins, the characteristics of one of the enzymes are quite similar to those of a lysosomal protease of the cathepsin-like type of enzyme and the other differs clearly from the acid protease and plasma kallikreins and has physicochemical characteristics quite similar to those of the kallikreins of glandular origin.