抄録
Plasma kallikrein is known as a hypotensive factor in blood, which originates from kallikreinogen, and its action is due to formation of plasma kinin from kininogen. On the activation of kallikreinogen and the kinin formation, highly complicated mechanisms have been proposed by several authors. In our previous studies (1, 2), it was reported that not only kallikrein but also plasmin release kinin directly from kininogen, and no conversion of kallikreinogen into kallikrein by purified plasmin was observed under our experimental conditions. Moreover, Hageman factor, which was purified from bovine plasma, could convert kallikreinogen into kllikrein, but not plasminogen into plasmin. From these results, it was suggested that kinin formation in plasma is due to the action of kallikrein activated by Hageman factor or contact factor, and plasmin activated by tissue activator or bacterial product, such as streptokinase.
On kininogen, it was found that in plasma there exist two types of kininogen, I andII, which are separated from each other with DEAE-Sephadex A-50 column chromatography (3): kininogen I is not adsorbed on the resin and kininogen II is adsorbed. Actions of various kinin forming enzymes on these two types of kininogen were examined and the kinin formed was determined by means of uterus of rat. Trypsin, plasmin and kallikrein activated by acetone treatment released kinin from both types of kininogen. However, the release of kinin from kininogen I by kallikrein activated by acetone was smaller than that from kininogen II. On the other hand, the kinin formation by kallikrein activated by Hageman factor was observed only from kininogen I and not from kininogen II. These results show the different kinin forming activities of these enzymes, and, particulary, between kallikrein activated by acetone treatment and that by Hageman factor.
Various animal tissues contain a kallikrein inhibitor, and that found in lung is known under the trade name of “Trasyrol”. In our present experiments, an inhibitor specific for kallikrein was observed in human plasma, and it was partially purified. The kallikrein inhibitor rapidly lost its activity at a temperature higher than 50°C. It was non-dialyzable, precipitated dy 0.6 saturation with ammonium sulfate, and has no effect on the esterolytic activity of plasmin. One KIU was designated as the amount of inhibitor which inhibits one mole of tosyl-L-arginine methyl ester TAMe hydrolyzing activity of kallikrein for 30min. at 37°C and pH 7.4. By using gel filtration of human plasma with Sephadex G-150, two types of kallikrein inhibitors were found. One was fastly eluated and inhibited TAMe hydrolytic activity of kallikrein (activated by acetone) specifically, and the other, which is lately eluated, inhibited the esterolytic activities of kallikrein and thrombin. The fast eluated fraction was applied to DEAE-cellulose column chromatography, and eluated with a gradient of increasing ionic strength using 0.017 M Tris, pH 7.3 and the same buffer containing 0.3 M NaCl. The specific activity of the most highly active fraction was 100 times of that of the original plasma. This purified kallikrein inhibitor decreases not only esterolytic activity of kallikrein but also hypotensive activity of kallikrein. Further studies will be required to elucidate the difference of this inhibitor from trasyrol and the inhibitor of C1-esterase in plasma.
