TABLE 2.

Parameters governing the action of prothrombinase on prothrombin variants

All fitted parameters are listed ± 95% confidence limits.

Substrate variant	Initial rate ± S.D.a	Normalized rate	Ks* ± S.D.b	KE,P ± S.D.	n ± S.D.	kcat320c
	μm/min/nm E			μm	mol of S/mol of E	s−1
IIWT	5.73 ± 0.66	1.0	0.018 ± 0.002	58.4 ± 5.1	1.04 ± 0.03	96
IIRR	5.10 ± 1.15	0.89	0.13 ± 0.01	62.5 ± 2.5	0.98 ± 0.02	97
IIRGR	4.65 ± 0.71	0.81	0.25 ± 0.01	58.8 ± 3.0	1.02 ± 0.04	100
II-1δ	3.93 ± 0.47	0.69	0.31 ± 0.01	45.9 ± 0.9	1.20 ± 0.02	89
II-2δ	2.65 ± 0.61	0.46	0.41 ± 0.01	57.6 ± 1.6	1.03 ± 0.02	66
II-3δ	0.80 ± 0.25	0.14	0.88 ± 0.03	54.5 ± 2.0	1.08 ± 0.03	0
II-4δ	0.69 ± 0.24	0.12	3.4 ± 0.12	69.4 ± 2.5	0.90 ± 0.03	0
IIQ320	0.24 ± 0.08	0.04	4.3 ± 0.11	69.7 ± 1.7	0.90 ± 0.02	0

^a Initial rates represent those for the total rate of prothrombin consumption determined from progress curves illustrated in Fig. 4.

^b Fitted parameters determined from fluorescence binding measurements with pAB represent the unimolecular equilibrium constant for active site docking (wherein K_s* = k₋/k₊), the equilibrium dissociation constant for the binding of the probe to prothrombinase assembled with Xa_S195A (K_E,_P), and the stoichiometry reflecting moles of substrate engaging the active site at saturation.

^c k_cat320 reflects the intrinsic k_cat for the action of prothrombinase in the 320 region and was calculated from initial rate using Equation 1.