The effect of Pep1 on the rFXIII-A₂*–mediated incorporation of glutamine-donor peptide biotinyl-TVQQEL to lysine-acceptor sites on plates coated with (A) fibrin and (B) poly-L-lysine in the presence of Pep1. A master mix containing 0.5 mM biotinyl-TVQQEL peptide, 0.1 mM DTT, 10 mM calcium, 1 U/mL human α-thrombin in 100 mM NaCl, 50 mM Tris at pH 7.4 was added to wells coated with fibrin (A) or poly-L-lysine (B) and containing 5.5 µg/mL FXIII-A₂ in the presence (▪) or absence (●) of Pep1 (final concentration, 55.2 µM). Samples were performed in triplicate (n = 3), and the results are expressed as means (SEM).