Table 2.

Inhibition of factor X activation by intrinsic Xase by active site–directed ligand

Kinetic constants obtained from initial velocity studies conducted with varying concentrations of factor X with different fixed concentrations of 4-aminobenzamidine. Studies were done using 14 different concentrations of factor X (0–0.3 μm), four different fixed concentrations of pAB (0, 75, 150, and 300 μm), and intrinsic Xase assembled using 0.1 nm IXa, 15 nm VIIIa, and 30 μm PCPS ([E] = 0.1 nm).

Inhibition typea	V/Eb	Km	Ki	αc
	s−1	nm	µm
Noncompetitive	2.07 ± 0.04	39.4 ± 2.6	163 ± 11	0.52 ± 0.09
Noncompetitive	1.95 ± 0.04	40.2 ± 2.4	131 ± 8	0.37 ± 0.07
Noncompetitive	2.12 ± 0.04	48.1 ± 3.2	161 ± 9	0.34 ± 0.08

^aOther forms of reversible inhibition were eliminated by analysis according to alternate rate expressions as described “under Data Analysis”.

^bKinetic constants are reported ± 95% confidence limits.

^cMultiplier for K_m at saturating pAB and for K_i at saturating factor X.