Table 1.

Kinetics and binding affinity of soluble human ACE2 and RBD-Ig variants

	kon (M−1 s−1)	koff (s−1)	Ka (M−1)	Kd (M)
TOR2	7.12 × 104	1.16 × 10−3	6.20 × 107	1.62 × 10−8
K344R	6.50 × 104	1.04 × 10−3	6.27 × 107	1.60 × 10−8
F360S	6.23 × 104	8.80 × 10−4	7.08 × 107	1.41 × 10−8
N479K	5.73 × 104	2.77 × 10−2	2.07 × 106	4.84 × 10−7
T487S	3.88 × 104	1.37 × 10−2	2.84 × 106	3.52 × 10−7
SZ3	42.6	2.35 × 10−2	1.81 × 103	5.51 × 10−4
Surface plasmon resonance experiments in which the indicated RBD-Ig TOR2 variants shown in Figure 6B bound to immobilized anti-human antibody were assayed for association with soluble human ACE2. The Experiment is representative of two performed with similar results.