The conversion of human prothrombin to thrombin is associated with a number of cleavage intermediates and products whose appearance and concentration are dependent upon the prothrombin activation conditions used. In the current investigation, the fragments of prothrombin which appear in normal human plasma after activation of the blood coagulation cascade were studied. Radioiodinated human prothrombin was added to platelet-poor relipidated normal human plasma and clotting initiated with Ca(II) and kaolin. The radiolabeled prothrombin cleavage products which formed were analyzed by polyacrylamide gel electrophoresis in the presence of dodecyl sulfate (SDS) and 2-mercaptoethanol (2-ME), A new product of prothrombin activation was observed. Its migration was more rapid than prethrombin 1 and slower than fragment 1.2. No previously identified products of prothrombin activation migrated to the same position in the gel.The previously unrecognized fragment was identified as fragment 1.2.3 as follows. Prothrombin was activated by factor Xa in the presence of Ca(II) and phospholipid. The desired product was isolated by absorption to and elution from barium citrate and by DEAE cellulose chromatography. This purified material, migrating identically with the unknown plasma product was homogeneous upon SDS gel electrophoresis with 2-ME. The amino terminal sequence of the isolated material was identical to that of prothrombin. Digestion of this material with either factor Xa or thrombin yielded as major products fragment 1.2 and fragment 1. (Fragment 2 and fragment 3 eluted from the gels under the conditions employed). Amino terminal sequence analysis of the factor Xa digestion products of the isolated material indicated three amino acid residues at each cycle. The sequences of fragment 1, fragment 2, and fragment 3 are consistent with this sequence analysis. On this basis we suggest that fragment 1.2.3 is a prominent product of prothrombin conversion to thrombin in plasma.
Purification and amino-terminal sequence analysis of the complement-fixing and precipitin antigens from Coccidioides immitis.
