[Kinetics and mechanism of individual and combined oxidation of o-dianisidine and bismuthol I by hydrogen peroxide catalyzed by horseradish peroxidase].

The individual and combined oxidation of 5-mercapto-1,3,4-thiadiazolthione-2 (bismuthol I) and 3,3'-dimethoxybenzidine (o-dianisidine) by hydrogen peroxide catalyzed by horseradish peroxidase (pH 5,0) was studied. It was shown that bismuthol I is a substrate for peroxidase, which is competitive towards o-dianisidine. In the presence of bismuthol I the Km value for o-dianisidine is increased, while kappa cat remains unchanged. The competitive inhibition constant for bismuthol is equal to 19,4 mkM. An addition of bismuthol I causes the appearance of the induction period (tau) on the kinetic curves of o-dianisidine oxidation, whose duration is proportional to bismuthol concentration. The kinetic patterns allowing interpretation of the experimental results are proposed. A kinetic analysis permitted to determine the rate constants for the individual steps of omicron-dianisidine oxidation catalyzed by peroxidase.