Electrochemical Assay of Oxidoreductase Enzymes
Because many coenzymes are electroactive this property can be used to provide an electrical signal related to the activity of a corresponding oxidoreductase enzyme. An example of the coupling of an enzymatic reaction and an electrochemical reaction involves the coenzyme NAD (1). The NADH is oxidized to NAD+ at the anode and within the surrounding electrolyte solution. The enzyme alcohol dehydrogenase (ADH) catalyzes the reduction of NAD+ to NADH by ethanol. If the electrolyte solution contains at first only NAD+ and ethanol but no enzyme, then neither enzymatic nor electrochemical reaction will occur until enzyme is added. It is this electrochemical reaction which starts only after addition of enzyme, which is the basis for the assay methods to be described.