Modeling of Biochemical Nitrate Reduction in Constant Electric Field

T. Parvanova-Mancheva, V. Beschkov and T. Sapundzhiev

Abstract
Experiments on the bioelectrochemical stimulation of enzyme reduction of nitrate to nitrite in a potentiostatic regime at different catode potentials were carried out. It was established that the stimulation effect of the constant electric field on nitrate reduction is also relevant for cell-free enzyme preparation, i.e. the effect is related to the constitutive enzymes nitrate-reductase and nitrite-reductase, contained in the cell membranes. Mathematical modeling of these experimental data as well as data for the same process accomplished by living immobilized cells was carried out. The purpose of the modeling was to select the most suitable kinetic model and then estimate the kinetic parameters and their dependence on the cathode potential. The mathematical models were based on the Michaelis-Menten kinetics taking into account inhibition by nitrate and nitrite. This modeling helped to conclude that the stimulation consists of two effects: enhanced maximum rate of nitrate enzyme reduction and faster nitrite reduction to eliminate nitrite inhibition on the overall process. It was found that the maximum reaction rates of nitrate and nitrite reduction depend on the cathode potential with maxima at + 0.01 V vs. the saturated hydrogen electrode.

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Keywords
Nitrate reduction, enzyme process, cell-fee crude extract, bacterial cells, bioelectrochemical stimulation