The Polydisulfide of Gallic Acid Is a Highly Effective Inhibitor of Peroxidase Reactions

E. I. Karasyova,¹ Yu. P. Losev,² and D. I. Metelitza^1,3

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

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

³To whom correspondence should be addressed.

Submitted February 25, 1997; revision submitted June 16, 1997.

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The polydisulfide of gallic acid (PDGA) effectively inhibits peroxidation of tetramethylbenzidine (TMB) at 20°C in 0.01 M phosphate buffer, pH 6.4. However, PDGA is a poor inhibitor of peroxidation of ortho-phenylenediamine (PDA) in the same buffer at pH 5.8 because of peroxidase-dependent co-oxidation of the PDA--PDGA couple. PDA peroxidation was inhibited by sodium (2,3-dihydroxy-4,6-di-tert-butyl-phenyl)-S-thiosulfate with moderate efficiency (K_i = 4.7·10^-4 M). The inhibition constant of TMB peroxidation by PDGA at 20°C was 1.3·10^-6 M. At moderate concentrations (0.01-0.1 mM) PDGA can be used for termination of peroxidase-dependent TMB oxidation, and this is important for the practice of enzyme immunoassay. The characteristics of co-oxidation of couples aromatic amine (substrate)--substituted phenol (inhibitor) catalyzed by peroxidase are discussed.

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KEY WORDS: peroxidase, peroxidase inhibitors, polydisulfide of gallic acid, substituted pyrocatechols, bioantioxidant, o-phenylenediamine, tetramethylbenzidine, co-oxidation of amines and phenols.

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