THE POLYDISULFIDE OF GALLIC ACID IS A HIGHLY EFFECTIVE INHIBITOR OF PEROXIDASE REACTIONS

The polydisulfide of gallic acid (PDGA) effectively inhibits peroxidat ion of tetramethylbenzidine (TMB) at 20 degrees C in 0.01 M phosphate buffer, pH 6.3. However, PDGA isa poor inhibitor of peroxidation of or tho-phenylenediamine (PDA) in the same buffer at pH 5.8 because of per oxidase-dependent co-oxidation of the PDA-PDGA couple, PDA peroxidatio n was inhibited by sodium (2,3-dihydroxy-4,6-di-tert-butyl-4 phenyl)-S -thiosulfate with moderate efficiency (K-i = 4.7.10(-4) M), The inhibi tion constant of TMB peroxidation by PDGA at 20 degrees C was 1.3.10(- 6) M. At moderate concentrations (0.01-0.1 mM) PDGA can be used for te rmination of peroxidase-dependent TMB oxidation, and this is important for the practice of enzyme immunoassay. The characteristics of co-oxi dation of couples aromatic amine (substrate)-substituted phenol (inhib itor) catalyzed by peroxidase are discussed.