Kinetics of the irreversible inhibition of catalase by 3-amino-1,2,4-triazole in the presence of hydrogen peroxide and catalase-hydrogen peroxide complex I hydrogen donors.

The irreversible inhibition of catalase by 3-amino-l, 2,4-trizole and a group of related inhibitors (1) in the presence of a continuous supply of hydrogen peroxide has been shown to result from a reaction of the inhibitors with catalase-hydrogen peroxide complex I (2) in which 1 mole of inhibitor is incorporated into the enzyme protein for each mole of catalase heme that has reacted (1). The kinetic equations describing these reactions have been derived (3). When, in addition to catalase, hydrogen peroxide, and an irreversible inhibitor of the 3-amino-l, 2,4-triazole series, the system also contains a catalase-hydrogen peroxide complex I hydrogen donor, i.e. a substance that can be oxidized by catalase-hydrogen peroxide complex I, the hydrogen donor will compete with the inhibitor for catalase-hydrogen peroxide complex I, and the rate of irreversible inhibition will be correspondingly decreased. Moreover, the kinetic situation will differ from that in which no hydrogen donor is present, since the “peroxidatic” rather than the “catalatic” action of catalase will be involved (4). A partial solution of the kinetic equation describing this system that did not allow any experimental confirmation has been presented (5). The present paper is concerned with a complete solution of the kinetic equation describing the initial rate of irreversible inhibition of catalase by an inhibitor of the a-amino1,2,4-triazole series in the presence of a continuous supply of hydrogen peroxide and a suitable hydrogen donor. An experimental verification of this equation is given.