Glucose Oxidase-Mediated Reduction Processes: H2 Evolution, Hydrogenation of Acetylene, and Reduction of NO3− by Glucose

Abstract

The application of enzymes as catalysts for biotechnological and bioelectronic products has found growing scientific interest. Numerous chemical transformations are catalyzed by redox-active enzymes, for example, the reduction of substrates by cofactor-dependent dehydrogenases or the oxidation of substrates by oxidases. Similarly, many redox-enzyme-functionalized electrodes were implemented to assemble electrochemical sensors, for example, glucose oxidase or alcohol dehydrogenase sensing electrodes. A fundamental issue in the application of redox proteins in bioelectronic devices or biocatalytic transformations is the need for the redox center of the enzyme to electrically communicate with the macroscopic environment. Although redox mediators (diffusional or covalently linked to the proteins) act as effective electrically contacting units connecting the enzyme redox centers with the electrodes, redox enzymes that utilize diffusional cofactors, such as the nicotinamide adenine dinucleotide couple NAD/NADH, require the electrochemical regeneration of the cofactors to activate the bioelectrocatalytic processes. Herein, we apply the electrical contacting paradigm of redox enzymes by electron relay units for the activation of non-native biocatalytic transformations. Specifically, we highlight that an oxidase (glucose oxidase) can drive new biocatalytic transformations under anaerobic conditions that do not occur in nature. We demonstrate that the coupling of the electron mediator N,N’-dimethyl-4,4’bipyridinium to the glucose oxidase (GOx) enzyme catalyzes the oxidation of glucose and transforms the enzyme into an electrically contacted assembly that leads to either hydrogen evolution, hydrogenation, and reduction of NO3 to NO2 . Besides demonstrating the use of glucose as an electron source for the hydrogenation/reduction processes, we anticipate that the transformation of an oxidase into a hydrogenase, through the application of the electrical contacting principles, might offer a useful general paradigm for future biotechnology. The system consists of GOx, the substrate glucose, N,N’-dimethyl4,4’-bipyridinium (MV), which acts as an electron mediator under anaerobic conditions (Scheme 1). The time-dependent absorbance changes of the system that includes GOx, MV, and glucose under anaerobic conditions is shown in Figure 1A. The time-dependent buildup of the spectrum of the N,N’-dimethyl-4,4’-bipyridinium radical cation (MVC) is observed, and the buildup reaches a saturation value after approximately 400 min, which corresponds with the equi-