Competitive inhibition assay displaying the effect of synthetic peptides Pep1 (▪), Pep1-E396A (▲), Pep1-Cys (X), and Cys-Pep1 (●) on the binding of rFXIII-A₂* to recombinant αC fragment 1 (Aα233-425). rFXIII-A₂* (0.5 µM) was preincubated with increasing concentrations of each peptide (0.5-250 µM) and added to wells coated with recombinant fibrin αC fragment 233-425 (αF1). Bound rFXIII-A₂* was detected using an HRP-conjugated anti–FXIII-A antibody and OPD substrate at an absorbance of 490 nm. The optical density was converted to percentage of FXIII-A₂ binding to αF1. Samples were performed in triplicate (n = 3). Error bars show ± 1 standard deviation (SD).