Energy conservation and maximal entropy production in enzyme reactions

•Density of entropy production in a two-step enzyme reaction is maximized.•Mass conservation and fixed products of forward and backward enzyme rate constants are used as optimisation constraints.•Model accounts for the conditions in a continuous stirred tank reactor.•Optimal values of rate constants are calculated for Glucose Isomerase (GI).•GI in open system possibly operates close to the maximum in density of entropy production.

A procedure for maximization of the density of entropy production in a single stationary two-step enzyme reaction is developed. Under the constraints of mass conservation, fixed equilibrium constant of a reaction and fixed products of forward and backward enzyme rate constants the existence of maximum in the density of entropy production is demonstrated. In the state with maximal density of entropy production the optimal enzyme rate constants, the stationary concentrations of the substrate and the product, the stationary product yield as well as the stationary reaction flux are calculated. The test, whether these calculated values of the reaction parameters are consistent with their corresponding measured values, is performed for the enzyme Glucose Isomerase. It is found that calculated and measured rate constants agree within an order of magnitude, whereas the calculated reaction flux and the product yield differ from their corresponding measured values for less than 20 % and 5 %, respectively. This indicates that the enzyme Glucose Isomerase, considered in a non-equilibrium stationary state, as found in experiments using the continuous stirred tank reactors, possibly operates close to the state with the maximum in the density of entropy production.

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