Significance of uricase in oxidase-induced oxidative coloring reaction of p-phenylenediamine

Uricase (mate oxidase, UOD) is found to induce the oxidative polymerization of p-phenylenediamine (PPD) effectively, which is a key reaction of color development in hair-dyeing and fur-dyeing practices. The significance of uricase is described by comparison to glucose oxidase (GOD), which also produces hydrogen peroxide as an oxidizing agent of PPD. In contrast to UOD, GOD inhibits the polymerization reaction. Spectroscopic and electrochemical study has revealed that the inhibition effect of GOD is ascribed to the glucose dehydrogenase activity, in which p-benzoquinonediimine (BQI) as the two-electron oxidized form of PPD works as an efficient electron acceptor to be reduced back to PPD, resulting in the inhibition of the subsequent polymerization of BQL. On the other hand, the UOD reaction does not compete with the polymerization of BQI owing to the lack of urate dehydrogenase activity in UOD. In addition, it has been found that UOD catalyzes the oxidation of PPD in the presence of uric acid by PPD oxidase-like and PPD peroxidase-like activities. These properties of UOD are favorable toward the oxidative generation of BQI from PPD and are responsible for the prominent ability in the oxidative coloring of PPD.