HORSERADISH PEROXIDASE-CATALYZED HYDROXYLATION OF PHENOL .1. THERMODYNAMIC ANALYSIS

We analyzed the horseradish peroxidase (HRP)-catalyzed hydroxylation o f phenol in the presence of dihydroxy-fumaric acid and oxygen. All of the intermediate forms of the enzyme are reviewed. The last step of hy droxylation, consisting of the production of OH. radicals that further react on phenol, is emphasized. Possible OB radicals production react ions were compiled and analyzed with respect to the available thermody namic data. Some results of electrochemical experiments were also used to choose the correct set of reactions. At the end of analysis only t wo reactions for producing OH. seemed to be consistent with the thermo dynamic and experimental data. Neither of these reactions involved com pound III or any other intermediate form of HRP. The last step of hydr oxylation was thus totally independent of the pure catalytic cycle of the enzyme. As a consequence, HRP cannot be used as an hydroxylation e nzyme in place of the P-450 cytochrome, as is sometimes suggested.