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=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 k(cat) and high K-M value of the ADH used) necessitating higher than theoretical methanol concentrations.