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SUMMARY In this work the dependency of reaction activation energy on reduction potential of substrates was investigated, as well as the influence of pre-exponential factor from Arrhenius equation on different compounds. Twelve compounds, having various structural features, were employed: (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid, N,N-dimethyl-4-(morpholin-4-yl)aniline, 2,6-dichlorophenolindophenol, 4,4'-(1,4-phenylene)bis(morpholine), 10-(2-hydroxyethyl)phenoxazine, N,N’-dimethyl-4,4’-azopyridinium hexafluorophosphate, methylene blue, Meldola's Blue, N-methylphenazonium methyl sulphate, sodium phenoxazine propiosulphate, thionine, N,N,N′,N′-tetramethyl-p-phenylenediamine). The candidates were selected so that they would have a clearly defined mechanism of reduction and their reduction products would be stable for the length of measurement. The compounds had their reduction potentials determined by cyclic voltammetry, also reduction rate constant and activation energy of the reaction in catalysis by Aspergillus niger glucose oxidase were measured. Reaction rate constants have been determined from experimental curves reflecting the formation of reduction product, described by proposed system of differential equations. Reaction rate constants had been calculated at six different temperatures (10 °C, 15 °C, 20 °C, 25 °C, 30 °C and 35 °C), relevant for calculation of activation energies from Arrhenius equation. Accordingly, it was concluded that activation energy of glucose oxidase catalyzed reduction reaction depends on the reduction potential of substrate. By comparing dependencies of enzymatic reaction rate constants and reaction activation energies on reduction potential of substrate, it was concluded that pre-exponential factor may not be the same for all of the compounds capable of participating in bimolecular catalysis reaction. Moreover, a clear relationship between compound structure and enzyme active center was determined. During the electron transfer, the consecutive electron and proton transfer takes place, this fact is supported by the proposed mathematical description, which thoroughly approximates the experimental results. |
