Products of prothrombin activation. (A) Sodium dodecyl sulfate-polyacrylamide gel showing recombinant prothrombin (II) and recombinant prothrombin with alanine substitutions for Arg¹⁵⁵, Arg²⁷¹, and Arg²⁸⁴ (Mz). The latter has been converted to the active protease Mz-IIa by incubating with ecarin. The numbers to the right of the gel indicate the amino acids contained in the 2 major fragments of Mz-IIa. The schematic diagram to the right shows conversion of prothrombin to α-thrombin, with the intermediates Mz-IIa and Mz-IIa(desF1), and are labeled using a numbering system for human prothrombin. (B) Nonreducing SDS-polyacrylamide gel showing preparations of α-IIa, β-IIa, and γ-IIa, relative to prothrombin (II). In the schematic diagram to the right, the proteases are labeled using separate numbering systems for the human α-IIa A1′ and B chains. For α-IIa, the corresponding numbers for the prothrombin numbering system (top) are shown for comparison. Gels in both panels were stained with Coomassie blue, and the positions of molecular mass standards in kilodaltons are shown to the left of the gels.