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The peroxidase-catalyzed oxidation of 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS), o-phenylenediamine (PDA), and 3,3′,5,5′-tetramethylbenzidine (TMB) was found to be activated by tetrazole and 5-aminotetrazole (AT) and weakly inhibited by 1,5-diaminotetrazole. The activating action of tetrazole and AT on the PDA and TMB oxidation was clearly discompetitive and that on ABTS was non-competitive. The coefficients (degrees) of activation α were determined for three substrates and two activators; they depended on the substrate type and the buffer nature and increased along with the pH growth from 6.4 to 7.2. For AT and tetrazole, the maximal α values were 4140 and 800 M–1, respectively, upon the PDA oxidation and 3570 and 540 M–1, respectively, upon the TMB oxidation. Lower α values (145 and 58 M–1 for tetrazole and AT, respectively) were characteristic of the peroxidase oxidation of ABTS. The activation of peroxidase oxidation of the substrates by tetrazole and AT at pH ≥ 5.4 was explained by the nucleophilic nature of the activators interacting with the amino acid residues in the peroxidase active site according to the mechanism of acid–base catalysis. |
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