The effects of different concentrations of 2-amino-4-nitrophenol (ANP) and of its polydisulfide (poly(ADSNP)) on peroxidase-catalyzed oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) were studied at 20 degrees C in reversed micelles of AOT (0.2 M) in heptane and in mixed reversed micelles of AOT (0.1 M)-Triton X-100 (0.1 M) in isooctane supplemented with 15% hexanol. The oxidation of TMB was activated nearly twofold in the presence of ANP and nearly fourfold in the presence of poly(ADSNP) in reversed micelles of AOT, whereas in the mixed micelles oxidation of the TMB-ANP pair was associated with inhibition of TMB conversion and poly(ADSNP) activated oxidation of TMB. The co-oxidation of TMB with 4,4'-dihydroxydiphenylsulfone (DDS) and with its polydisulfide (poly(DSDDS)) at different concentrations of phenol components was accompanied by activation of TMB conversion in 0.01 M phosphate buffer (pH 6.4) supplemented with 5% DMF and in reversed micelles of AOT in heptane. The effect of pH of the aqueous solution on the initial oxidation rate of the TMB-DDS and TMB-poly(DSDDS) pairs and also the effect of hydration degree of reversed micelles of AOT on conversion of the same pairs by peroxidase were studied. A scheme of peroxidase-dependent co-oxidation of "aromatic amine-phenol" pairs is proposed and discussed. A significant part of this scheme is a nonenzymatic exchange of phenoxyl radicals with amines and of aminyl radicals with phenols.

The peroxidase-catalyzed oxidation of 3,3;,5,5;-tetramethylbenzidine (TMB), ortho-phenylenediamine (PDA), and 5-aminosalicylic acid (5-ASA) is significantly accelerated in the presence of 2-aminothiazole (AT) and melamine (MA), and an increase in their concentrations is associated with a parallel increase in the k(cat) and K(m) values for TMB and PDA. The activation of the peroxidase-catalyzed oxidation of TMB and PDA is quantitatively characterized by a coefficient (degree) alpha (M(-1)) which significantly depends on pH in the range 6.2-6.4, 6.4-7.4, and 6.0-7.4 for the TMB-AT, TMB-MA, and PDA-MA pairs, respectively. An increase in the coefficient alpha with increase in pH confirms nucleophilicity of activation of the peroxidase-catalyzed oxidation of the aromatic amines in the presence of AT and MA. Under optimal conditions the coefficients alpha for the TMB-AT, PDA-AT, TMB-MA, and PDA-MA pairs vary in the limits of (1.90-3.53)*10(3) M(-1).

No abstract