Cationic Proteins of Human Granulocytes V. Interaction with Plasma Protease Inhibitors

Abstract

Several cationic proteins of human granulocytes possess chymotrypsin-like and bactericidal activities. The heat-labile chymotrypsin-like activity is inhibited by serum, owing to complex formation with .alpha.2-macroglobulin and .alpha.1-antitrypsin. The molar affinity of the cationic proteins for .alpha.2-macroglobulin is much higher than that for .alpha.1-antitrypsin. The molar combining ratios are 1:1 for cationic protein to .alpha.1-antitrypsin and 2:1 for cationic protein to .alpha.2-macroglobulin. The proteolytic activity against fibrinogen and casein is inhibited by both .alpha.2-macroglobulin and .alpha.1-antitrypsin but the activity against small molecular synthetic substrates is inhibited by .alpha.1-antitrypsin but not .alpha.2-macroglobulin. The heat-stable bactericidal action of the cationic proteins against Staphylococcus was also inhibited by serum, probably owing to complex formation with .alpha.2-macroglobulin and .alpha.1-antitrypsin.