Inhibition of proteases by KRK α₁AT. SDS-PAGE of the reactions of (A) APC, (B) thrombin, and (C) fXa with KRK α₁AT. Native serpin is indicated by a solid arrow, cleaved serpin by an open arrow, and the covalent serpin:protease complex by a shaded arrow. (A) and (B) are run under nonreducing conditions, and (C) is run under reducing conditions. In each gel, lane M shows molecular weight markers, lane 2 is the protease alone, lane 3 is KRK α₁AT alone, and the other lanes are the reactions at the indicated times.