Abstract
Chymotryptic cleavage of human prothrombin produces two fragments, prothrombin (des 1–44) previously characterized and peptide 1–41. This peptide has been purified by barium citrate adsorption and Sephadex G100 chromatography. It contains the 10 γ-carboxyglutamic residues of prothrombin. Added to a prothrombin activation mixture containing FXa, phospholipid and Ca ++, peptide 1–41 inhibits thrombin generation with the same potency as prothrombin fragment 1. Ca ++ produces a 20 % quenching of the intrinsic fluorescence of the peptide. So do Mn ++ and Mg ++ although to a lesser extent. Phospholipid enhances the Ca ++ induced quenching by a factor of 1.7 and shifts the midpoint of the transition from 0.34 to 0.46 mM Ca ++. The major difference with titration curves obtained with prothrombin F1 is the absence of cooperativity. Hence peptide 1–44 has retained some of the prothrombin properties to interact with Ca ++ and phospholipid and represents the vitamin K dependent domain of the molecule. The presence of the remaining part of F1 (residues 44–155) however is necessary for the expression of cooperativity.
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