Structure of Horseradish Perosidase Compound I

The kinetics of the reaction between horseradish peroxidase and p-nitroperbenzoic acid to form compound I have been studied at 25 degrees C in phosphate buffer pH 7.2 and ionic strength of 0.11 M by transient-state and steady-state methods. The second-order rate constant for compound I formation obtained by stopped-flow measurements at 403 nm is (3.7 +/- 0.2) x 10(7) M-1 s-1. For the disappearance of p-nitroperbenzoic acid and appearance of p-nitrobenzoic acid using steady-state kinetics measured at 265 nm the rate constant is (3.0 +/- 0.6) x 10(7) M-1 s-1. The results provide an independent confirmation that one and only one oxygen atom is incorporated from the oxidizing substrate into compound I.