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In vitro metabolic engineering of bioelectricity generation by the complete oxidation of glucose

Zhu, Zhiguang, Zhang, Y.-H. Percival
Metabolic engineering 2017 v.39 pp. 110-116
NAD (coenzyme), pentose phosphate cycle, electrons, NADP-glucose-6-phosphate dehydrogenase, glucose, electrodes, adenosine triphosphate, electron transfer, gluconeogenesis, biohydrogen, metabolic engineering, biofuels, glucose 6-phosphate, oxidation, bioelectricity, phosphorylation, glucokinase, phosphogluconate dehydrogenase
The direct generation of electricity from the most abundant renewable sugar, glucose, is an appealing alternative to the production of liquid biofuels and biohydrogen. However, enzyme-catalyzed bioelectricity generation from glucose suffers from low yields due to the incomplete oxidation of the six-carbon compound glucose via one or few enzymes. Here, we demonstrate a synthetic ATP- and CoA-free 12-enzyme pathway to implement the complete oxidation of glucose in vitro. This pathway is comprised of glucose phosphorylation via polyphosphate glucokinase, NADH generation catalyzed by glucose 6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH), electron transfer from NADH to the anode, and glucose 6-phosphate regeneration via the non-oxidative pentose phosphate pathway and gluconeogenesis. The faraday efficiency from glucose to electrons via this pathway was as high as 98.8%, suggesting the generation of nearly 24 electrons per molecule of glucose. The generated current density was greatly increased from 2.8 to 6.9mAcm⁻² by replacing a low-activity G6PDH with a high-activity G6PDH and introducing a new enzyme, 6-phosphogluconolactonase, between G6PDH and 6PGDH. These results suggest the great potential of high-yield bioelectricity generation through in vitro metabolic engineering.