Peroxidase activity of ferritin in aerosol OT reversed micelles in heptane

Using oxidation of o-phenylenediamine (PDA) and tetramethylbenzidine (TMB) by hydrogen peroxide, cumene peroxide (CHP), tert-butyl hydroperoxide (TBHP), and Triton X-45 hydroperoxide (Triton X-45-HP), the peroxidase activity of horse spleen ferritin was investigated in reversed micelles of aerosol OT (AOT) in heptane with various hydration degrees. With hydrogen peroxide as oxidant the dependences of initial rate of oxidation of both substrates (v0) on hydration degree W0 are characterized by maxima at W0 = 9-11, 20, and 41. In the system containing TBHP--ferritin these maxima were not observed. The parameters kcat, Km, and their ratios kcat/Km as a criterion of ferritin efficiency in peroxidase reactions were determined for both substrates in micellar medium at various W0. Increase of W0 was accompanied by a decrease of kcat and Km. With hydrogen peroxide the peroxidase activity of ferritin in the AOT micelles was significantly lower than in 0.1 M acetate buffer, pH 4.2. However, the efficiency (expressed as kcat/Km) of a system ferritin--Triton X-45-HP in micellar TMB oxidation exceeded that in the aqueous medium. A method of purification of iron-containing crystallite from the ferritin molecule was developed using reversed AOT micelles in heptane and heating the mixture on a water bath.