The binding of FXIII-A₂B₂ to fibrinogen, fibrin, and fibrinogen αC region 371-425 (fragment 9) by SPR. Increasing concentrations of FXIII-A₂B₂ (0.7-200nM) activated in the presence of 5 U/mL biotinylated thrombin and 1.5mM calcium [a₂b₂], or 5 U/mL thrombin in the presence of 5mM EDTA [Thr-A₂B₂], or nonactivated FXIII-A₂B₂ in the presence of 5mM EDTA [nonactivated A₂B₂], were injected over (A) GST α fragment 9, (B) fibrinogen, and (C) fibrin for 120 seconds (dissociation time, 120 seconds) at a flow rate of 30 μL/min. SPR running buffers contained 140mM NaCl, 20mM HEPES, 0.05% P20, and either 1.5mM calcium or 5mM EDTA, pH 7.4. Regeneration of binding was achieved with two 50-second injections of 2M NaCl for captured GST α fragment 9 binding the FXIII-A₂B₂ activation variants, and two 40-second injections of 5mM NaOH containing 100mM NaCl at a flow rate of 30 μL/min for interactions between fibrin(ogen) and the FXIII-A₂B₂ activation variants (n = 3). The SPR sensorgrams for the binding of FXIII-A₂B₂ to GSTα fragment 1 were indistinguishable from the binding to GSTα fragment 9; therefore, they are not shown. All sensorgrams shown are representative of one experiment from triplicate runs (n = 3).