Kinetic investigations of horseradish peroxidase in AOT/n-heptane reverse micelles

The oxidation of typical horseradish peroxidase substrate, 2,2'-azino-bis[3-ethyl-benzothiazoline-(6)-sulfonic acid] (ABTS), has been studied in AOT/n-heptane reverse micelles. The rate of product formation has been found to be over an order of magnitude higher in reverse micelles than in homogeneous aqueous solution. The rate constants of all three elementary steps of horseradish peroxidase reaction with ABTS are higher in reverse micelles than in homogeneous aqueous solution. The rate limiting step of compound I formation is the exchange between enzyme filled and hydrogen peroxide filled micelles. The exchange step most probably also influences the rate of ABTS reactions with compound I and compound II, although the changes in their rate constants due to a different water and enzyme structure in reverse micelles cannot be excluded.