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Full-time dynamics of batch-wise enzymatic cycling system composed of two kinds of dehydrogenase mediated by NAD(P)H for mass production of chiral hydroxyl compounds

Yamane, Tsuneo
Journal of bioscience and bioengineering 2019 v.128 no.3 pp. 337-343
NAD (coenzyme), NADP (coenzyme), carbonyl compounds, enzymatic reactions, enzymes, equations
Enzymatic cycling system (coupled dehydrogenase-catalyzed biosystem being composed of two elementary enzymatic reactions mediated by NAD(P)H + NAD(P)+) is industrially attractive for reducing prochiral carbonyl compounds to the corresponding chiral hydroxyl compounds. The reaction rate equation of the batch-wise biosystem was generally derived by ordered Bi Bi mechanism of two-substrate enzyme reaction on several reasonable assumptions. The rate equations of the batch-wise biosystem was generalized by transforming them into the dimensionless forms. The dimensionless forms were solved numerically. It was revealed that the batch-wise biosystem was generally made up of unique 3 phases, i.e., phases I, II and III. Phase I was very short transient so that the biosystem entered rapidly phase II. In phase II the consumption rate dynamically balanced with its formation rate so that the concentration of NAD(P)H was invariable with time (and hence NAD(P)+ concentration was, too). Phase III was substrate-exhausting phase, and the coenzyme concentration became finally only [NAD(P)+] or only [NAD(P)H] depending on the initial molar ratio of the prochiral carbonyl compound to the substrate of the coenzyme regeneration reaction ([S]0/[S′]0) > or <1.0. In phases I and II the numerically calculated values of state variables were very close to the analytical but approximate ones. Preferable initial conditions of the batch-wise enzymatic cycling system, i.e., the initial coenzyme species = NAD(P)+ and [S]0/[S′]0<1.0, were proposed. As the main assumption irreversibility of the two elemental enzymatic reactions was discussed. Validity of the proposed rate equations was mentioned.