Kinetics of the inhibition of human factor Xa by full-length and truncated recombinant tissue factor pathway inhibitor

Theo Lindhout*, George Willems, Ron Blezer, H. Coenraad Hemker

*Corresponding author for this work

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    The inhibition equilibrium and kinetics of association and dissociation of the binding of three types of recombinant tissue factor pathway inhibitor (TFPI), namely full-length TFPI, C-terminal-truncated TFPI, and TFPI without the third Kunitz domain (TFPI1-161), Xa have been measured. Formation and dissociation of the complexes were monitored by continuous measurement of the changes in the rate of hydrolysis of a peptidyl-p-nitroanilide substrate. Progress curves of product formation were fitted to a set of equations describing a one-step bimolecular inhibitory reaction in the presence of a competing substrate. For full-length TFPI the rate constants of association (k(on)) and association (k(off)) were (5.1+/-0.7)x10(6) M(-l.) s(-l) and (2.6+/-0.9)x10(-4) s(-1) respectively. Thus, although the inhibition constant (50 pM) is far below the plasma concentration (2.5 nM) of TFPI, the half-time for transition to equilibrium in plasma is rather long (66 s). The truncated forms of TFPI differ in that they have a 4-fold lower k(on) value but a similar dissociation rate constant. Therefore the inhibition constant, K-i, is 4-fold higher (0.2 nM) and the half-time to achieve equilibrium is prolonged to 250 s. The k(on) values of full-length and C-terminal-truncated TFPI, but not that of TFPI1-161, were found to decrease with increasing ionic strength.
    Original languageEnglish
    Pages (from-to)131-136
    Number of pages6
    JournalBiochemical Journal
    Issue number1
    Publication statusPublished - 1 Jan 1994

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