Role of the Apoprotein in the Catalytic Peroxidase-Like Function of Ferritin

G. S. Arapova,¹ A. N. Eryomin,¹ and D. I. Metelitza^1,2

¹Institute of Bioorganic Chemistry, National Academy of Sciences of Belarus, Zhodinskaya ul. 5/2, Minsk, 220141 Belarus; fax: (0172) 63-7274; E-mail: ibochbel@ns.igs.ac.by

²To whom correspondence should be addressed.

Submitted June 10, 1997; revision submitted July 30, 1997.

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The thermal inactivation of horse spleen ferritin was studied over a range of temperatures (36-52°C) in 0.1 M acetate buffer (pH 4.2) as a decrease of its peroxidase activity during tetramethylbenzidine (TMB) oxidation by hydrogen peroxide. The activation energy of this process was 163.3 kJ/mole. Thermodynamic activation parameters for the loss of peroxidase activity of ferritin were calculated. The influence of various detergents on ferritin-dependent oxidation of TMB, ortho-tolidine, and ortho-phenylenediamine (PDA) by hydrogen peroxide was studied in 0.1 M phosphate buffer (pH 6.0) at 20°C. Relatively high concentrations of charged detergents (SDS and cetyltrimethylammonium bromide) decreased the peroxidase activity of ferritin with all three amines, whereas moderate concentrations of the nonionic detergent Triton X-100 did not influence oxidation of these substrates. Increase of dimethylformamide concentration in 0.02 M acetate buffer (pH 4.2) from 5 to 40% strongly decreased the rate of TMB and PDA oxidation by hydrogen peroxide or cumene hydroperoxide. Decrease in the activity of thermally inactivated ferritin with TMB as substrate, reduction of alpha-helical content of the protein at 40-50°C, an inactivating effect of charged surfactants and organic co-solvent on the peroxidase activity of ferritin indicate a very important role of the apoprotein in peroxidase function. A possible mechanism of apoferritin participation in peroxidase catalysis is discussed.

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KEY WORDS: ferritin, apoferritin, peroxidase activity of ferritin, thermal inactivation of ferritin, influence of detergents on activity, role of apoferritin in catalysis.

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