Table 4. Kinetic and affinity constants of the monovalent V_HHs and the bivalent V_HH2-Fc antibody against α–Cbtx as measured by surface plasmon resonance (SPR).

Antibody	KD (nM)c	k on (M−1s−1)	k off (s−1)
VHH C2	0.4	5.2×105	1.9×10−4
VHH C43	24	2.9×105	6.8×10−3
VHH C19	25	5.8×105	1.0×10−2
VHH C20	1	1.8×106	1.7×10−3
VHH2-Fc antibody	N/A	N/A	5.0×10−5

^cEquilibrium dissociation constants K_D (k _off/k _on), association (k _on) and dissociation (k _off) rate constants.