Interactions of alpha-1-antichymotrypsin, alpha-1-proteinase inhibitor, and alpha-2-macroglobulin with the fungal enzyme, seaprose.

The Semi-alkaline proteinase (Seaprose) from Aspergillus melleus has been tested for its ability to either inactivate or form complexes with three human plasma proteinase inhibitors, alpha-2-macroglobulin, alpha-1-antichymotrypsin and alpha-1-proteinase inhibitor. alpha-2-Macroglobulin was found to inhibit Seaprose, with two mol of enzyme being complexed per mol of inhibitor. However, alpha-1-proteinase inhibitor was rapidly inactivated by the fungal enzyme as a result of cleavage of the inhibitor, primarily at the P1-P'1 reactive site. Curiously, alpha-1-antichymotrypsin was found to form complexes with Seaprose and also be inactivated by this inhibitor. Apparently, the enzyme can recognize two sites within the reactive site loop of the inhibitor, one at the P4-P'5 position, resulting in inactivation, and one presumably at the P1-P'1 reactive site which results in complex formation. The fact that Seaprose can so rapidly inactivate alpha-1-proteinase inhibitor, the primary regulator of neutrophil elastase, indicates that Seaprose would be a rather poor choice for therapy in individuals with bronchial mucus hypersecretion.