STUDIES ON INHIBITION OF NEUTROPHIL CATHEPSIN-G BY ALPHA(1)-ANTICHYMOTRYPSIN

alpha(1)-Antichymotrypsin, a member of the serpin family of serine pro teinase inhibitors, has been reported to inhibit chymotrypsin by a mod ified version of the suicide substrate reaction mechanism operative fo r other serpins. To investigate if this mechanism is also applicable t o the inhibition of cathepsin G by this serpin, the effect of temperat ure on the reaction between cathepsin G and alpha(1)-antichymotrypsin has been examined by SDS-PAGE and stoichiometric titrations. At 0 degr ees C, a cathepsin G-alpha(1)-antichymotrypsin complex of Mr 89,250 is formed which, at 38 degrees C, was cleaved by free enzyme to give a s table complex of Mr 80,250. The reaction stoichiometry at 0 degrees C was 1.53, which decreased to 1.30 at 38 degrees C, consistent with an decrease in the substrate pathway. These data are compatible with the modified suicide substrate reaction scheme. The formation of three pro ducts (cleaved inhibitor and two forms of complex) from the reaction a nd the potential for differential product formation suggests that modu lation of the suicide substrate mechanism may play a role in the regul ation of inflammatory processes mediated by cathepsin G.