Intramolecular Synergism of the Inhibiting Action of Polydisulfide Antioxidants in the System Ferritin--H₂O₂--Tetramethylbenzidine

D. I. Metelitza^1*, G. S. Arapova¹, A. N. Eryomin¹, and Yu. P. Losev²

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

²School of Chemistry, Belorussian State University, ul. Leningradskaya 14, Minsk, 220080 Belarus; fax: (0172) 26-5942

^* To whom correspondence should be addressed.

Received February 18, 1999

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Polydisulfides of urea (PDSU), thiourea (PDSTU), biuret (PDSB), and gallic acid (PDSG) and their monomer analogues (urea, biuret, and gallic acid) inhibited (in a competitive manner) tetramethylbenzidine (TMB) peroxidation catalyzed by ferritin in 0.1 M acetate buffer, pH 4.2, containing 10% dimethylformamide. Their efficiency characterized in terms of inhibition constants, K_i, increased in the following order PDSU < PDSB ~ PDSTU << PDSG. This order is determined by the reactivity of monomers with respect to HO^· radicals which are the main oxidizing agents in the system ferritin--H₂O₂. Polydisulfide antioxidants exhibit the intramolecular synergism of the inhibiting action (non-additivity of antiradical activity relative to their monomers) that was quantitatively characterized by alpha = (K_i)_pol/(K_i)_mon·n, where n is the number of monomers in the polymeric inhibitors. The alpha values increased from 1.5 up to 5.18 in the following order: PDSG < PDSU < PDSB. Significantly higher inhibiting efficiency of polydisulfide antioxidants as compared to monomer forms and synergism of the inhibitory action offer promising opportunities of their use as quenchers of free radical processes in biochemical systems.

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KEY WORDS: ferritin, hydrogen peroxide, polydisulfide antioxidants, synergism of inhibitors, intramolecular synergism, tetramethylbenzidine

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