TABLE 3.

Kinetics of heparin-catalyzed reactions of native and prelatent antithrombins with thrombin and factor Xa Kinetic parameters were obtained from fits of the data of Figs. 6 and 7 for high affinity heparin and low affinity heparin-catalyzed reactions of native and prelatent antithrombins with thrombin or factor Xa by the ternary complex bridging or conformational activation models described under “Experimental Procedures.” The fitted parameters were the rate constant for the reaction of heparin-complexed antithrombin with protease (k_H) and the dissociation constants for the binary antithrombin-heparin complex (K_AT,H) and the protease-heparin binary complex (K_Pr,H).

Antithrombin	Protease	kH	KAT,H	KPr,H
		m–1 s–1	m	m
High affinity heparin-catalyzed reactions
Native	IIa	4.5 ± 0.3 × 107	2.0 ± 1.2 × 10–9	1.2 ± 0.4 × 10–6
Prelatent	IIa	5.0 ± 0.4 × 107	11 ± 3 × 10–9	0.91 ± 0.25 × 10–6
Native	FXa	2.3 ± 0.6 × 106	3.5 ± 1.0 × 10–9	10 ± 2 × 10–6
Prelatent	FXa	2.1 ± 0.8 × 106	8.4 ± 2.0 × 10–9	15 ± 5 × 10–6
Low affinity heparin-catalyzed reactions
Native	IIa	6.4 ± 0.3 × 105	12 ± 2 × 10–5	3.6 ± 0.6 × 10–7
Prelatent	IIa	7.0 ± 0.2 × 105	8.5 ± 0.9 × 10–5	3.5 ± 0.3 × 10–7
Native	FXa	5.4 ± 0.2 × 105	2.2 ± 0.2 × 10–5
Prelatent	FXa	4.0 ± 0.3 × 105	1.7 ± 0.3 × 10–5