Inhibition of Human Trypsin, Plasmin, and Thrombin by Naturally Occurring Inhibitors of Proteolytic Enzymes

Human trypsin was strongly inhibited by three apparently unrelated inhibitors: lima bean trypsin inhibitor, bovine colostrum inhibitor, and bovine Kunitz pancreatic inhibitor. It was inhibited to varying degrees by Kunitz soybean inhibitor, soybean inhibitor AA, kidney bean inhibitor, black-eyed pea inhibitor, navy bean inhibitor, and quail ovomucoid. It was essentially uninhibited by bovine Kazal pancreatic inhibitor, porcine Kazal pancreatic inhibitor, potato inhibitor, chicken ovoinhibitor, and 10 avian ovomucoids including that of chicken. Many of these proteins strongly inhibit bovine trypsin. Thus, inhibition of bovine trypsin by naturally occurring inhibitors is no index of their activities against human trypsin. The activities of these inhibitors against human plasmin were generally similar to those against human trypsin, except that the activities of lima bean inhibitor and quail ovomucoid were comparatively weaker and the activity of the Kunitz soybean inhibitor was much stronger. The esterolytic activity of human thrombin was not affected by any of the inhibitors.