Amino acid sequence of human prothrombin fragments 1 and 2.

The amino acid sequence of the nonthrombin half of human prothrombin is presented. Prothrombin fragment 1 has 155 amino acid residues as compared with 156 for the bovine equivalent. Ten gamma-carboxyglutamic acid residues are at the same location in each species. Human prothrombin fragment 2 contains 118 amino acid residues, as does the similar bovine fragment. Comparing bovine and human prothrombin fragment 1 we found 131 residues to be identical (84%). In prothrombin fragment 2, 84 residues were identical (71%). Assuming a time span of 90 million years since the radiation of several orders of placental mammals, prothrombin fragments 1 and 2 incorporated one substitution site per 100 amino acid sites every 11.2 and 6.3 million years, respectively. Internal homology is acribed to partial gene duplication, with the most likely crossover point located between residues 60-61 and residues 165-166.