CHEMBL5738604

Isopeptidase Assay for Estimating Inhibitor Potency: FXIIIa activity has been determined using substrate A101 (Zedira GmbH, Darmstadt, Germany), which is based on the N-terminal dodecapeptide of α2-antipiasmin. FXIIIa catalyzes by its isopeptidase activity the release of dark quencher dinitrophenyl at the original substrate glutamine position resulting in fluorescence increase (based on the N-terminal 2-aminobenzoyl fluorescent dye) (Oertel K, HunfekJ A, Specker E, Reiff C, Seitz R, Pasternack R, Dodt J. A highly sensitive fluorometric assay for determination of human coagulation factor XIII in plasma. Anal Biochem 2007; 367:152-8.)Briefly, 12 μL recombinant cFXIII-A2 (T027, Zedira GmbH, Darmstadt, Germany) or FXIII-A2B2 derived from human plasma (T007) (25 μg/mL) and 3 μL human α-thrombin (0.5 U/mL, T056, Zedira) were mixed with 270 μL assay buffer (50 mM Tris-HCl, 10 mM CaCl2), 150 mM NaCl, 5.56 mM glycine methyl ester, 5 mM DTT, pH 7.5) containing 55 μM A101 substrate. The mixture was incubated for 20 min at room temperature to activate FXIII. 15 μL of inhibitor solution (serial dilution from 1.25 μM to 1.25 nM) dissolved in DMSO/assay buffer were added, mixed and the kinetic measurement started after 3 min. Fluorescence emission was monitored at 418 nm (λex=313 nm) and 37° C. for 30 min using a CLARIOstar fluorescence micro plate reader (BMG Labtech, Ortenberg, Germany). For measurements without inhibitor, 15 μL of assay buffer/2% (v/v) DMSO were added. All measurements were performed in triplicate. The respective IC50 values were calculated by non-linear regression using the MARS software package (BMG Labtech).