Comparative aspects of prothrombin activation

The activation of the purified prothrombins from human, bovine, and chicken species have been studied. Chicken prothrombin activation, similar to bovine prothrombin, resulted in the formation of a 161 residue prothrombin fragment 1, a 113 residue prothrombin fragment 2, and chicken thrombin with a 49 residue A chain and a B chain of approximately 260 residues. When human prothrombin is converted to thrombin, the resulting thrombin is shorter from the amino-terminus of the A chain by 13 residues (human prothrombin fragment 3). The vitamin K-dependent regions of all three species are very similar in sequence (33 of 46 residues identical for all three species). The regions of internal homology observed within the human and bovine fragments are apparently also present within the chicken fragments, indicating that the partial gene duplication which resulted in the evolution of a prothrombin molecule of greater size than the other vitamin K-dependent coagulation proteins occurred prior to the divergence of birds and mammals over 300 million years ago.