TABLE 1.

Kinetics of wild-type, cysteine-free “wild-type,” and K239 variant ZPI inhibition of factor Xa and factor XIa

Rate constants and stoichiometries for ZPI-factor Xa and ZPI-factor XIa reactions in I 0.15, pH 7.4 Tris buffer at 25 °C were measured in the presence of PZ, calcium, and membrane cofactors for factor Xa reactions and in the absence of cofactors for factor XIa reactions as described under “Experimental Procedures.” Apparent second order rate constants were obtained from the slopes of the linear dependence of pseudo-first order rate constants on ZPI concentration in the range of 15–300 nm. The product of the apparent association rate constant (k_app) and SI represents the corrected association rate constant for reaction through the inhibitory pathway.

ZPI	Factor Xa reactions			Factor XIa reactions
	kapp	SI	kapp × SI	kapp	SI	kapp × SI
	m−1 s−1		m−1 s−1	m−1 s−1		m−1 s−1
Wild typea	3.1 ± 0.1 × 106	2.8 ± 0.2	8.7 ± 0.9 × 106	14.0 ± 0.1 × 104	8.0 ± 0.3	11.0 ± 0.1 × 105
C169A/C264S	4.7 ± 0.1 × 106	3.7 ± 0.1	17.4 ± 0.8 × 106	6.4 ± 0.9 × 104	9.4 ± 0.3	6.0 ± 1.0 × 105
+K239C	4.8 ± 0.5 × 106	3.5 ± 0.1	16.8 ± 2.2 × 106	11.0 ± 0.1 × 104	10.4 ± 0.1	11.4 ± 0.2 × 105
+K239C-NBD	2.6 ± 0.5 × 106	3.1 ± 0.2	8.1 ± 2.1 × 106	6.2 ± 0.6 × 104	11.0 ± 0.2	6.8 ± 0.8 × 105
+K239C-DANS	2.8 ± 0.1 × 106	2.9 ± 0.1	8.1 ± 0.6 × 106	9.5 ± 1.5 × 104	9.4 ± 0.2	8.9 ± 1.6 × 105
K239Aa	2.4 ± 0.1 × 106	4.2 ± 0.1	10.1 ± 0.7 × 106	14.0 ± 0.1 × 104	8.7 ± 0.4	12.2 ± 0.6 × 105

^a Taken from Ref. 18. The K239A variant retains the two wild-type cysteines.