Complete enzymatic oxidation of methanol to carbon dioxide: towards more eco-efficient regeneration systems for reduced nicotinamide cofactors

A novel system for in situ regeneration of reduced nicotinamide cofactors (NADH) is proposed: through a cascade of alcohol dehydrogenase (ADH), formaldehyde dismutase (FDM) and formate dehydrogenase (FDH) complete oxidation of methanol to carbon dioxide (CO2) is coupled to the regeneration of NADH. As a consequence, from one equivalent of methanol three equivalents of NADH can be obtained. The feasibility of this cascade is demonstrated at the examples of an NADH-dependent reduction of conjugated C[DOUBLE BOND]C-double bonds (catalysed by an enoate reductase) and the NADH-dependent hydroxylation of phenols (catalysed by a monooxygenase). The major limitation of the current regeneration system is the comparably poor catalytic efficiency of the methanol oxidation step (low kcat and high KM value of the ADH used) necessitating higher than theoretical methanol concentrations.