Table 1. Measure of the dissociation constant (Kd) of ACE2 bound to immobilized SARS-CoV or SARS-CoV-2 S proteins by surface plasmon resonance (SPR) or biolayer interferometry binding (BLI) approaches.

Reference	ACE2 protein PD domain	SARS-CoV S	SARS-CoV2 S	Method	Measured kd
Wrapp et al., 2020	1–615 aa	306–577 aa		SPR	325.8 nM
			1–1208 aa		14.7 nM
Wang et al., 2020a	19–615 aa	306–527 aa		SPR	408.7 nM
			319–541 aa		133.3 nM
Lan et al., 2020	19–615 aa	306–527 aa		SPR	31.6 nM
			319–541 aa		4.7 nM
Walls et al., 2020	1–614 aa	306–575 aa		BLI	1.2 nM
			328–533 aa		5 nM
Wrapp et al., 2020	1–615 aa	306–577 aa		BLI	13.7 nM
			319–591 aa		34.6 nM