TABLE 1.

Summary of fitted association and dissociation constants for the ACE2 interactions^a

Ligand	Analyte	kon (M−1 s−1)	koff (s−1)	Kdkin (nM)
ACE2-Fc	RBD	3.8 × 105	0.016	43
	S-R/x2	6.3 × 103	3.3 × 10−4	52
	S-R	1.0 × 105 (fast)	3.6 × 10−5	0.36
		1.5 × 104 (slow)		2.4
	S-R/PP	1.3 × 105 (fast)	7.4 × 10−5	0.57
		1.9 × 104 (slow)		3.9

^aFitted association (k_on) and dissociation (k_off) constants are shown. K_d^kin, the kinetic dissociation constant, is equal to k_off/k_on from concentration dilution series (see Fig. 2).