(A) α1-Antitrypsin was incubated at varying molar ratios with the model protease bovine α-chymotrypsin, and the residual protease activity determined. The intercept of the regression with the abscissa reflects the number of molecules of α1-antitrypsin required to inhibit one molecule of chymotrypsin in the presence (+c) and absence (-c) of 50µM GSK716. Error bars reflect ±SEM of three independent experiments. 