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  • Title: Characterization of proteases in AHF concentrates: effect on factor VIII:von Willebrand protein as assessed by high-pressure gel permeation chromatography.
    Author: Orthner CL.
    Journal: J Lab Clin Med; 1984 Nov; 104(5):816-28. PubMed ID: 6436416.
    Abstract:
    Antihemophilic factor concentrates were surveyed for amidolytic activity on the chromogenic substrates S2238, S2302, S2222, and S2251, which are sensitive to thrombin, kallikrein, factor Xa, and plasmin, respectively. For antihemophilic factor concentrates from two manufacturers, the rates of amidolysis of S2238 and S2302 were approximately an order of magnitude greater than the rates of amidolysis of S2222 and S2251. The S2238 and S2302 activities were characterized by quantitating their interactions with specific substrates or inhibitors. The Km for amidolysis of S2238 was 558 mumol/L, which is 80 times higher than for thrombin but in close agreement to the reported value for activated protein C. The S2238 activity was not inhibited by the thrombin-specific inhibitor dansylarginine N-(3-ethyl-1,5-pentanediyl)amide, nor by soybean trypsin inhibitor or micromolar concentrations of antithrombin III in the presence of heparin. The S2238 activity was inhibited by D-Phe-Pro-Arg-CH2Cl, but with an estimated second-order rate constant of 3 X 10(5) mol/L-1 minute-1, approximately 1000 times less than for thrombin. These data are consistent with the identity of the S2238 activity as activated protein C. On the other hand, the S2302 activity in antihemophilic factor concentrates was most likely attributable to kallikrein. This was based on the agreement with authentic kallikrein of the Km for S2302 of 154 mumol/L as well as by the rapid inactivation by nanomolar concentrations of the kallikrein-specific inhibitor D-Phe-Phe-Arg-CH2Cl. However, the relative resistance of the S2302 activity to inhibition by soybean trypsin inhibitor or antithrombin III and the partial inhibition by aprotinin suggested that a large proportion of the kallikrein was bound to alpha 2-macroglobulin. This was confirmed by immunoprecipitation using specific anti alpha 2-macroglobulin IgG. The potential for proteolysis of factor VIII:von Willebrand protein during its purification from antihemophilic factor concentrates was demonstrated, and the proteolyzed factor VIII coagulant species was characterized. High-pressure gel permeation chromatography of purified factor VIII:von Willebrand protein at high ionic strength resulted in two sharp peaks of factor VIII procoagulant activity. The earlier eluting peak corresponded with the void volume, and the later peak eluted with an apparent molecular weight of 53,000 daltons. Immediately after separation, the 53,000-dalton factor VIII coagulant had at least a 100-fold higher specific activity than the factor VIII coagulant present in the void volume. However, the 53,000-dalton factor VIII coagulant was labile, with a half-life of 80 minutes.(ABSTRACT TRUNCATED AT 400 WORDS)
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