(E) Representative curves reporting the interaction of different concentrations of GSK716 with Z α1-antitrypsin based on changes in intrinsic tryptophan fluorescence. Based on the concentration dependence (inset), the second-order rate constant of association was found to be 4.1 x 104 M-1 s-1. (F) The association of GSK716 with M α1-antitrypsin, giving a second-order rate constant of 2.1 x 102 M-1 s-1. 