Studies on inhibition of neutrophil cathepsin G by alpha 1-antichymotrypsin.

alpha 1-Antichymotrypsin, a member of the serpin family of serine proteinase inhibitors, has been reported to inhibit chymotrypsin by a modified version of the suicide substrate reaction mechanism operative for other serpins. To investigate if this mechanism is also applicable to the inhibition of cathepsin G by this serpin, the effect of temperature on the reaction between cathepsin G and alpha 1-antichymotrypsin has been examined by SDS-PAGE and stoichiometric titrations. At 0 degree C, a cathepsin G-alpha 1-antichymotrypsin complex of M(r) 89,250 is formed which, at 38 degrees C, was cleaved by free enzyme to give a stable complex of M(r) 80,250. The reaction stoichiometry at 0 degree 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 products (cleaved inhibitor and two forms of complex) from the reaction and the potential for differential product formation suggests that modulation of the suicide substrate mechanism may play a role in the regulation of inflammatory processes mediated by cathepsin G.