NAD-dependent glucose dehydrogenase

A large number of these systems, often indamine, phenazine, and phenoxazine phe-nothiazine dyes (for examples see Fig. 19), have been studied mostly in the context of the development of an amperometric biosensor for glucose using the NAD -dependent glucose dehydrogenase. The literature up to 1994 has been reviewed [8,115]. 

NAD-dependent glucose dehydrogenase, NAD-GDH, generally has good substrate specificity, but its cofactor is not bound and must be included as part of the strip reagent matrix as an additional component. Also, the number of effective mediators for NAD-GDH-based systems is more limited due the specific requirements for rapid reaction of the mediator with NADH (e.g., quinones and quinoid compounds). 

Schematic of the polyol pathway showing the NADPH-dependent reduction of open chain D-glucose to sorbitol, which is catalyzed by ALR2. This step is followed by the NAD+-dependent oxidation of sorbitol by sorbitol dehydrogenase to yield D-fructose.

An alternative biosensor system has been developed by Hart et al. [44] which involves the use of the NAD+-dependent GDH enzyme. The first step of the reaction scheme involves the enzymatic reduction of NAD+ to NADH, which is bought about by the action of GDH on glucose. The analytical signal arises from the electrocatalytic oxidation of NADH back to NAD+ in the presence of the electrocatalyst Meldola s Blue (MB), at a potential of only 0Y. Biosensors utilising this mediator have been reviewed elsewhere [1,17]. Razumiene et al. [45] employed a similar system using both GDH and alcohol dehydrogenase with the cofactor pyrroloquinoline quinone (PQQ), the oxidation of which was mediated by a ferrocene derivative. 

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