Role of the reductant substrates on the inactivation of horseradish peroxidase by m-chloroperoxybenzoic acid.

Horseradish peroxidase reacts with H2O2 and other hydroperoxides to form Compound I, the first active enzymatic form m-Chloroperoxybenzoic acid, a xenobiotic hydroperoxide, acts as an oxidant substrate of horseradish peroxidase. However, this hydroperoxide is also a powerful inactivator of the enzyme and in this sense is more effective than H2O2. The coupled reductant substrates used in the peroxidatic reaction protect the enzyme from the inactivating process. A reaction mechanism is proposed with two competitive routes: one catalytic and one inactivating. Using a kinetic approach, the ratio between the hydroperoxide and the reductant substrate appears to be a decisive factor in the catalytic turnover of the enzyme. The role of the reductant substrates in protecting the enzyme, and the physiological and biotechnological implications of this process are discussed.