Peroxidase Activity of Ferritin in Aerosol OT Reversed Micelles in Heptane

G. S. Arapova, A. N. Eryomin, and D. I. Metelitza^*

Institute of Bioorganic Chemistry, National Academy of Sciences of Belarus, ul. Zhodinskaya 5/2, Minsk, 220141 Belarus; fax: (0172) 63-7274; E-mail: ibochbel@ns.igs.ac.by

^* To whom correspondence should be addressed.

Received November 10, 1997

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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 k_cat, K_m, and their ratios k_cat/K_m 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 k_cat and K_m. 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 k_cat/K_m) 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.

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KEY WORDS: ferritin, reversed micelles, aerosol OT, peroxidase activity,

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