Inhibition of Mast Cell Chymase by Eglin c and Antileukoprotease (HUSI-I). Indications for Potential Biological Functions of these Inhibitors

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Abstract
Recominant elgin c (originally isolated from the medical leech) and antileukoprotease (HUSI-I from human seminal plasma) were examined for their ability to inhibit the mast cell protease chymase. Both inhibitors react rapidly with the enzyme: when about equimolar concentrations (in the range of 10-8 M) of chymase and HUSI-I or elgin c were incubated the complex formation was apparently at equilibrium after 1 or 5 min, respectively. When a constant amount of chymase (.apprxeq. 3 .times. 10-8 M) was incubated with increasing concentrations of inhibitor a concentration of HUSI-I of 7 .times. 10-7 M was necessary to cause 50% inhibition of the initial enzyme activity, whereas 8 .times. 10-8 M eglin c was sufficient. The dissociation constant of the chymase-elgin c complex was calculated to be 4.4 .times. 10-8 M. These results are discussed with respect to the possible in vivo function of antileukoproteaase as an inhibitor of mast cell chymase.