The role of micelles in mediator-assisted peroxidase catalysis

To elucidate the role of micelles in mediator-assisted peroxidase catalysis the oxidation of N-benzoyl leucomethylene blue (BMB) was performed in the presence of Triton X-100, sodium dodecyl sulfate (SDS) or cetyltrimethylammonium bromide (CTAB) at pH 8.5. Recombinant Coprinus cinereus peroxidase was used as an enzyme. It was shown that oxidation of BMB proceeded at high peroxidase concentration. The addition of 10-phenothiazine propionic acid (PPA) increased the oxidation rate of BMB tremendously and the rate was almost linearly dependent on PPA concentration. The action of PPA was explained by mediation of BMB oxidation with the cation radical of PPA. An increase in the surfactant concentration decreased the rate of both the direct and the mediator-assisted BMB oxidation. The results were analyzed by assuming an enzymatic reaction in the aqueous pseudophase. The calculated distribution coefficient between the micellar and the aqueous phases varied from 28 to 1770 and from 11 to 2200 for BMB and PPA, respectively. The constant of PPA oxidation in the aqueous phase of Triton X-100 micelles fitted an independently determined value in buffer solution, whereas in SDS micelles it was 4 times less. The decrease by 2 orders of magnitude of the constant in CTAB micelles was explained by micelle/substrate interaction and the PPA concentration in the micellar phase.