Table 1.

Association and dissociation rates and affinities of actoxumab binding to purified TcdA and its fragments as determined by SPR

Toxin/Kd (pM)a,b	fragment	kon (M−1 s−1)a,b	koff (sec−1)a,b
TcdA	1.87 × 105 ± 0.06 × 105	1.13 × 10−4 ± 0.13 × 10−4	610 ± 90
A1	5.92 × 105 ± 1.65 × 105	1.22 × 10−4 ± 2.01 × 10−4	220 ± 110
A4	3.19 × 105 ± 1.76 × 105	2.12 × 10−4 × 0.16 × 10−4	800 ± 490
TcdB	Not measurable	Not measurable	Not measurable

^aThe data presented are average ± standard deviation from two independent experiments.

^bk_off = dissociation binding constant; k_on = association binding constant; K_d = equilibrium dissociation constant.