The enzymatic activity of HRP was measured using an ABTS assay
in a CuBiAn XC enzymatic robot (Innovatis, Germany). 10 lL of
sample were mixed with 140 lL 1 mM ABTS solution (50 mM
potassium phosphate buffer, pH 6.5). The reaction mixture was
incubated at 37 C for 5 min before the reaction was started by
the addition of 20 lL 0.078% (w/w) H2O2. Changes in absorption
at 415 nm were measured for 80 s and rates were calculated. The
standard curve was prepared using a commercially available HRP
preparation (Type VI-A, Sigma–Aldrich, Austria) in the range from
0.02 to 2.0 U mL1.