Electrochemical bioreactor with regeneration of NAD+ by rotating graphite disk electrode with PMS adsorbed

Kinetic constants were compared among p-quinone, 2,6-dichlorophenolindophenol, phenazine methosulfate (PMS), methylene blue, and FAD in the oxidation of NADH. Among those, PMS was selected for its highest rate constant as a mediator for the electrochemical oxidation of NAD. The PMS could be stably immobilized on a graphite electrode surface by adsorption. The PMS adsorbed and that in the solution showed distinctly separated peaks in the cyclic voltammogram. The immobilized PMS functioned as an immobilized mediator to reduce the overpotential in the electrochemical oxidation of NAD so that the electrode could be used as an NAD regenerator. For the construction of an electrochemical bioreactor, a specially designed rotating disk graphite electrode was used. In spite of its extraordinarily large surface area, the behavior of the rotating disc electrode was described well by the Levich law. The NAD oxidation system of the rotating graphite disk electrode with PMS adsorbed was combined with glucose-6-phosphate dehydrogenase reaction, which reduced NAD with the consumption of glucose-6-phosphate. The electrochemical bioreactor system worked well with recycling of NAD at a high current efficiency.