Artificial, Photoinduced Activation of Nitrogenase Using Directed and Mediated Electron Transfer Processes

Matan M. Meirovich,Oren Bachar,Omer Yehezkeli

doi:10.3390/catal10090979

Matan M. Meirovich, Oren Bachar + Show 1 more

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https://doi.org/10.3390/catal10090979

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Abstract

Nitrogenase, a bacteria-based enzyme, is the sole enzyme that is able to generate ammonia by atmospheric nitrogen fixation. Thus, improved understanding of its utilization and developing methods to artificially activate it may contribute to basic research, as well as to the design of future artificial systems. Here, we present methods to artificially activate nitrogenase using photoinduced reactions. Two nitrogenase variants originating from Azotobacter vinelandii were examined using photoactivated CdS nanoparticles (NPs) capped with thioglycolic acid (TGA) or 2-mercaptoethanol (ME) ligands. The effect of methyl viologen (MV) as a redox mediator of hydrogen and ammonia generation was tested and analyzed. We further determined the NPs conductive band edges and their effect on the nitrogenase photoactivation. The nano-biohybrid systems comprising CdS NPs and nitrogenase were further imaged by transmission electron microscopy, visualizing their formation for the first time. Our results show that the ME-capped CdS NPs–nitrogenase enzyme biohybrid system with added MV as a redox mediator leads to a five-fold increase in the production of ammonia compared with the non-mediated biohybrid system; nevertheless, it stills lag behind the natural process rate. On the contrary, a maximal hydrogen generation amount was achieved by the αL158C MoFe-P and the ME-capped CdS NPs.

Highlights

Electrical communication between enzymes and their surroundings is tightly controlled by natural diffusional redox mediators [1,2,3,4,5]
We examined the role of different ligands and their effect on the role of the Fe protein (Fe-P) or its absence in artificial systems, the electron transfer process, the direct electron transfer process and the catalytic hydrogen and ammonia generation
NPs were modified with thioglycolic acid (TGA) acid or ME ligands, and their aptness to bind and activate nitrogenase was tested

Summary

Introduction

Electrical communication between enzymes and their surroundings is tightly controlled by natural diffusional redox mediators [1,2,3,4,5]. The outer shells of redox enzymes are insulators; they prevent short circuits with undesired electron carriers present in the surrounding. In the last several decades, the theoretical and experimental foundations of these processes were developed, improving our understanding thereof. Establishing electrical communication between redox proteins and electrodes or inorganic nanomaterials is a major challenge that has been at the forefront of research for the last two decades [7,8]. Using redox mediators or directed electron transfer configurations has led to a variety of sensing or energy generating devices

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