Effect of Antioxidants (Digoxin, Quercetin, and Ascorbic Acid) on Catalytic Properties of Horseradish Peroxidase

V. V. Rogozhin^* and V. V. Verkhoturov

Yakutsk State Agricultural Academy, ul. Krasil'nikova 15, Yakutsk, 677002 Russia; fax: (4112) 26-4949

^* To whom correspondence should be addressed.

Received September 11, 1997; Revision received November 10, 1997

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Antioxidants (digoxin, quercetin, and ascorbic acid) inhibited the oxidation of o-dianisidine catalyzed by horseradish peroxidase. Digoxin bound with the enzyme--substrate complex which included a stable semioxidized product of o-dianisidine and inhibited horseradish peroxidase by the anticompetitive pattern, while the enzyme inhibition by quercetin followed the mixed pattern. The oxidation of ascorbic acid and o-dianisidine with their combined presence in the reaction mixture was differentiated. o-Dianisidine was oxidized after the oxidation of 90-100% of ascorbic acid was completed. The rate of peroxidase oxidation of ascorbic acid in the presence of o-dianisidine was more than two orders higher than the rate of its individual oxidation and 1.5-2.0 times higher than the rate of o-dianisidine oxidation. Feasible inhibition mechanisms of peroxidase oxidation of o-dianisidine are discussed.

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KEY WORDS: horseradish peroxidase, ascorbic acid, o-dianisidine, digoxin, quercetin

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