In-situ regeneration of co-enzyme NADH with an electro-enzymatic biomimetic membrane

The biosynthesis of lactate from pyruvate has been used as a model system to demonstrate the applicability of electroenzymatic membrane reactors as electron transfer chain biomimetics. A key feature of this system is the in-situ regeneration of the co-enzyme NADH. This flow-by porous reactor utilizes an immobilized enzyme system (lipoamide dehydrogenase (LipDH) and methy viologen as a mediator) within porous graphite cathodes, encapsulated by a cation exchange membrane (Nafion(R) 124, Dupont). The free flowing fluid contains the pyruvatellactate (and co-products) reaction mixture, the enzyme lactate dehydrogenase (LDH) and the co-enzyme NADH/NAD⁺ system. Lactate yields up to 70% have been obtained when the reactor system was operated in a semi-batch (i.e. recirculation) made for 24 hours; as compared to only 50% when operated in a simple batch mode for 200 hours. The multipass, dynamic input operating scheme permitted optimization studies to be conducted on system parameters such as concentrations of all components in the free solution (initial and dynamic input values could be readily adjusted through recycle conditioning), flow rates and electrode composition as well as their transport characteristics. By varying the flow rates through this membrane reactor system, the authors identified the operating regimes that determine the controlling mechanism for process synthesis, i.e. mass transfer versus kinetics limitations, and developed procedures for operational map development