Association and dissociation of WT- and ΔK-scuPA from suPAR measured as surface plasmon resonance. Antihuman-uPAR monoclonal nonblocking antibodies were coupled to a CM5-research grade sensor chip flow cell. suPAR was captured for 2 minutes. Five minutes later, binding of WT-scuPA and ΔK-scuPA was measured for 2 minutes, followed by dissociation for 20 minutes. The bulk shift due to changes in refractive index measured on the monoclonal antibody/buffer surface was subtracted from the binding signal at each scuPA concentration to correct for nonspecific binding. Dissociation of suPAR from anti-uPAR antibodies, determined under the same conditions as scuPA, was also subtracted. The dose-response of scuPA (0.63 to 5 nM) binding to suPAR is shown. The lines represent a 1:1 interaction model of the binding of WT-scuPA during the association and dissociation phases. (A) WT-scuPA concentrations are 5, 2.5, 1.3, and 0.6 nM. (B) ΔK-scuPA concentrations are 10, 5, 2.5, and 1.3 nM. The lines represent the best global fit to a 1:1 binding model.