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Thromb Haemost 1979; 42(01): 412
DOI: 10.1055/s-0039-1687040
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The Nature of Factor VIIIC
Schattauer GmbH

Activation of Factor VIII by Thrombin as Measured by Competition Kinetics

H. Sandberg
1   Research Department, Biochemistry, Kabi AB, Stockholm, Sweden.
,
K. Brodén
1   Research Department, Biochemistry, Kabi AB, Stockholm, Sweden.
,
L.-O. Andersson
1   Research Department, Biochemistry, Kabi AB, Stockholm, Sweden.
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Publication Date:
26 April 2019 (online)

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It is known that the procoagulant activity of purified Factor VIII is strongly increased when incubated with concentrations of thrombin below 0.1 unit/ml. It has been assumed that this also is a mechanism of physiological importance thus that activation of Factor VIII by low concentrations of thrombin is one step in normal blood coagulation. The rate constant tor the reaction between Factor VIII and thrombin was estimated by two different methods. In one method formation of “activated” Factor VIII in a system containing thrombin, purified Factor VIII and albumin added as stabilizer was measured. In the other method the competition of purified Factor VIII as substrate for thrombin was compared with fibrinogen and a chromogenic peptide substrate. As expected it was found that thrombin had higher affinity for Factor VIII than for fibrinogen. The values calculated for the second order rate constant, using 240,000 as the molecular weight of the reactive unit in Factor VIII, were similar for the various systems, around 106s-1M-1.