Twelve amino acid sequences of kringle-forming polypeptides were compiled from the known sequences of urokinase A-chain (human), a tissue-type plasminogen activator (human), prothrombin (human and bo-vine), and plasminogen (human). Their sequence homologies with maximum match were examined by a computer program. A homology alignment and graphic matrix analyses did show that they had a great degree of homology. All the cystein residues responsible for the kringle structures of urokinase and the tissue-type plasminogen activator were confidently preserved as well as other proteins.
A phylogenetic tree was then reconstructed, and the A-and S-chain of bovine and human prothrombins were accounted for the measurement of the evolutionary time span. It was found that urokinase had a larger time span, as much as 60 million years (MY), than the tissue-type plasminogen activator. A common ancestral element of the kringle-related serine proteases was placed at around 500 MY ago, as old as the diversion of the α-and β-chains of hemoglobin. Thus, the kringle-families have undergone a substantial evolutionary divergence. Moreover, they can be subgrouped into three subfamilies : plasminogen activators, plasminogen, and prothrombin A-chains, the last being the most distantly diverged prothrombin S-chains.