Inactivation of α(2)-Macroglobulin by Activated Human Polymorphonuclear Leukocytes

The proteolytic activity of trypsin releases the dye Remazol Brilliant Blue from its high molecular weight substrate, the skin powder (Hide Powder Azure, Sigma), with an increase in absorbance at 595 nm. Active α(2)- macroglobulin (80 μg/ml) totally inhibits the proteolytic activity of trypsin (14 μg/ml) by trapping this protease. But after a 20 min incubation of α(2)-macroglobulin at 37°C with 2 × 10(6) human polymorphonuclear leukocytes activated by N-formyl-L-methionyl-L-leucyl-L-phenylalanine (10(−7) M) and cytochalasin B (10(−8) M), 100% of trypsin activity was recovered, indicating a total inactivation of α(2)-macroglobuHn. Incubation with granulocyte myeloperoxidase also inactivates α(2)-macroglobulin. Hypochlorous acid, a by-product of myeloperoxidase activity, at a concentration of 10(−7) M also inactivates α(2)-macroglobulin, which indicates that an important cause of α(2)-macroglobulin inactivation by activated polymorphonuclear leukocytes could be the activity of myeloperoxidase.