Affimer protein F5 reduced the rate of plasminogen to plasmin conversion. (A-B) The effect of Affimer F5 on plasminogen to plasmin conversion was studied in a plasmin generation assay. Fibrin clots were formed with fibrinogen (0.5 mg/mL) and increasing concentrations of Affimer F5 (Affimer:fibrinogen molar ratios of 1:1, 5:1, and 10:1) with scaffold-only protein included as a control. Clots were lysed by overlaying with tPA in the presence of S2251. (A) Increase in absorbance readings for the first 60 minutes of plasmin generation assays. (B) Plasmin generation presented as rate of chromogenic substrate hydrolysis (au/min). (C) Experiments were also performed without fibrin(ogen), while using the highest concentration of Affimer protein, to assess the fibrin(ogen)-specificity of Affimer F5. (D) In a purified turbidity and lysis assay, preformed clots with and without Affimer protein were overlaid with lysis mix containing either plasminogen–tPA or (E) plasmin. Numbers on the x-axis represent Affimer protein:fibrinogen molar ratios. Data are presented as the mean ± SD of 3 independent experiments. Statistical analysis was performed using 1-way ANOVA, **Difference from buffer-only control; P < .01.