Section: Chemistry of natural environments and objects
Tetrazolium salts are used in monitoring the ecological state of environmental objects, especially after exposure to factors unfavorable to organisms: forest fires, oil spills, industrial and household pollution. The possibility of identifying the indicator properties of iodinitrotetrazolium chloride (INT) to assess the viability of the aerobic bacterium Bacillus stearothermophilus is shown. The dependence of the concentration of the iodomonoformazane (IMF) reduction product on the exposure time at an optimal for the vital microorganisms’ activity temperature of 37 оC was studied as a criterion for quantifying the bacterium reducing ability in relation to a tetrazolium salt. The IMF concentration was determined spectrophotometrically at 490 nm wavelength after extraction of an aliquot of the reaction mixture with ethyl acetate. It was found that the reaction rate slows down when the reagent conversion reaches 60–70 %. It has been suggested that a decrease in the regenerative capacity of bacterial cells may be due to the IMF recovery product inhibitory effect. Formazane is less polar than INT, and has a greater affinity for cellular components. This argument suggests that IMF forms inactive complexes with cellular reducing agents. The blocking of cellular redox centers by the reduction product may be the main reason for the decrease in reagent conversion over time. A formal kinetic scheme of the IMF reduction reaction by cellular electron donors is proposed based on experimental data on the dependence of the IMF current concentration on the exposure time. According to the scheme, the reaction product does not selectively interact with cellular redox centers to form inactive complexes with an inhibition constant Ki. The scheme is processed by the diagram method based on the quasi-equilibrium approximation of kinetic scheme analysis. The integral kinetic equation in Walker-Schmidt coordinates, which are widely used in enzymatic catalysis, is obtained by the diagram method. The kinetic equation obtained is consistent with the experimental data. The numerical value of the inhibition constant by the product equal to (1.42 ± 0.12) . 10-5 M was determined.
Keywords: iodonitrotetrazolium chloride, Bacillus stearothermophilus, kinetic scheme of inhibition by the reaction product, diagram method, inhibition constant
Article published in number 2 for 2026 DOI: 10.25750/1995-4301-2026-2-137-144
ISSN 1995-4301
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