ACTIVATION OF HUMAN FACTOR-VII DURING CLOTTING INVITRO

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  • 1 January 1985
    • journal article
    • research article
    • Vol. 65  (1) , 218-226
Abstract
Factor VII activation was studied by measuring the ratio of factor VII clotting to coupled amidolytic activity (VIIc/VIIam) and cleavage of 125I-factor VII. In purified systems, a low concentration of Xa or a higher concentration of IXa rapidly activated 125I-factor VII, yielding a VIIc/VIIam ratio of 25 and similar gel profiles of heavy and light chain peaks of VIIa. On further incubation, VIIa activity diminisihed and a 3rd 125I-peak appeared. When normal blood containing added 125I-factor VII was clotted in a glass tube, the VIIc/VIIam ratio rose 5-fold, and 20% of the 125I-factor VII was cleaved. Clotting normal plasma in an activated partial thromboplastin time (APTT) system yielded a VIIc/VIIam ratio of 25 and over 90% cleavage of 125I-factor VII. Clotting factor XII-deficient plasma preincubated with antibodies to factor X in an APTT system with added XIa yielded a VIIc/VIIam ratio of 19 and about 60% cleavage, which indicates that IXa, at a concentration achievable in plasma, can effectively activate factor VII. Clotting normal plasma with undiluted tissue factor yielded a VIIc/VIIam ratio of 15-20 and 60% cleavage of 125I-factor VII, whereas clotting plasma with diluted tissue factor activated factor VII only minimally. Both Xa and IXa can function as significant activators of factor VII in in vitro clotting mixtures but only small amounts of factor VII may be activated in vivo during hemostasis.