Biochemical reaction engineering for redox reactions

Abstract

Redox reactions are still a challenge for biochemical engineers. A personal view for the development of this field is given. Cofactor regeneration was an obstacle for quite some time. The first technical breakthrough was achieved with the system formate/formate dehydrogenase for the regeneration of NADH2. In cases where the same enzyme could be used for chiral reduction as well as for cofactor regeneration, isopropanol as a hydrogen source proved to be beneficial. The coproduct (acetone) can be removed by pervaporation. Whole-cell reductions (often yeast reductions) can also be used. By proper biochemical reaction engineering, it is possible to apply these systems in a continuous way. By cloning a formate dehydrogenase and an oxidoreductase "designer bug" can be obtained where formate is used instead of glucose as the hydrogen source. Complex sequences of redox reactions can be established by pathway engineering with a focus on gene overexpression or with a focus on establishing non-natural pathways. The success of pathway engineering can be controlled by measuring cytosolic metabolite concentrations. The optimal exploitation of such systems calls for the integrated cooperation of classical and molecular biochemical engineering.

Synthesis, Characterization and Application of New Rhodium Complexes for Indirect Electrochemical Cofactor Regeneration

“…[9] To reduce the oxidised cofactor selectively, the electrochemical reduction is mediated by a rhodium catalyst, which lowers the necessary reduction potential and avoids unselective side reactions. [8] This mediator accepts two electrons at the cathode and after inserting a proton into its coordination sphere, the resulting hydride ion is transferred to the cofactor.…”

Productive Asymmetric Styrene Epoxidation Based on a Next Generation Electroenzymatic Methodology

“…The most efficient enzymatic methodologies in terms of productivities employ living microbial cells as biocatalysts, performing intracellular FADH 2 regeneration at the expense of energy sources such as glucose, [10,11] or isolated regeneration enzymes utilizing chemical sources of reduction equivalents such as formate. [12] Alternatively, electrical power, the cheapest source of reduction equivalents for redox enzymes, [13] can be used for the reagent-free regeneration of FADH 2 at cathodes in cell-free epoxidations, omitting the cellular cofactor regeneration machinery and additional regeneration enzymes from the reaction. [14] In general, such electroenzymatic approaches might not only be more practical because of their simplicity, but they would also combine two environmentally friendly methods for the selective synthesis of chiral synthons.…”

Process development for the electroenzymatic synthesis of (R)‐methylphenylsulfoxide by use of a 3‐dimensional electrode

“…The use of electrochemistry in redox biotransformation opens up new possibilities for biochemical engineering (Liese, 2005;Wandrey, 2004). Without the electrochemical investigations the role of the cosolvent would not have been questioned.…”