Cationic proteins of human granulocytes. V. Interaction with plasma protease inhibitors.

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 alpha2-macroglobulin and alpha1-antitrypsin. The molar affinity of the cationic proteins for alpha2-macroglobulin is much higher than that for alpha1-antitrypsin. The results indicate that the molar combining ratios are 1:1 for cationic protein to alpha1-antitrypsin and 2:1 for cationic protein to alpha2-macroglobulin. The proteolytic activity against fibrinogen and casein is inhibited by both alpha2-macroglobulin and alpha1-antitrypsin, whereas the activity against small molecular synthetic substrates is inhibited by alpha1-antitrypsin but not alpha2-macroglobulin. The heat-stable bactericidal action of the cationic proteins against Staphylococcus was also inhibited by serum, probably owing to complex formation with alpha2-macroglobulin and alpha1-antitrypsin.