Researchers connected a solar-powered chemical reaction to a sequence of enzyme reactions to make a sugar from carbon dioxide. The laboratory system produced L-sorbose, a sugar used as an intermediate in vitamin C manufacture, showing how electrical and biological catalysis can work together.
The study by Guangyu Liu and colleagues appeared in Nature Communications on 25 March 2024. It was a demonstration of chemical synthesis outside living cells, with enzymes performing the steps that built the sugar molecule.
From carbon dioxide to a six-carbon product
The system began with a photovoltaic panel illuminated by simulated sunlight. Its electricity powered an electrochemical reactor that converted carbon dioxide into formate, a molecule containing one carbon atom.
A five-enzyme system then carried out the biological part of the process. The reactions passed through formaldehyde and three-carbon intermediates before forming the six-carbon sugar L-sorbose.
The enzymes included an engineered phosphite dehydrogenase to help regenerate the cofactor NADH, along with enzymes that assembled smaller carbon compounds into larger ones. An altered fructose-6-phosphate aldolase, FSA A129S, catalysed the final carbon–carbon bond-forming step.
The name L-sorbose matters: the output was a particular chemical product, rather than ordinary table sugar or a nutritionally complete food.
Why separate the enzyme reactions?
Different catalytic steps have different requirements. The researchers arranged the biological reactions in three stirred vessels and used filtration membranes to retain enzymes while allowing products to move downstream.
That arrangement helped manage the flow of intermediates and limit interference between stages. It also allowed enzyme reuse during repeated operation.
The reported production rate reached 105 milligrams of L-sorbose per litre per hour from the second operating cycle under the study’s conditions. After five cycles, each reactor having operated for a total of 120 hours, the system retained 79.5% of its initial sugar yield.
What the 3.5% efficiency figure tells us
The authors reported a solar-to-sugar energy conversion efficiency of 3.5% and compared it with an approximately 1% natural-photosynthesis benchmark. That was the basis for the widely reported “more than three times” comparison.
It is a comparison within the study’s calculation, not evidence that this apparatus is three times more efficient than every crop or agricultural system. A complete production assessment would also need to account for equipment, enzyme manufacture, operating inputs and product recovery.
One input is particularly important: sodium phosphite supplied reducing power for cofactor regeneration. The paper estimated that making one kilogram of L-sorbose consumed 6.1 kilograms of sodium phosphite, producing a phosphate by-product. Sunlight and carbon dioxide were therefore not the system’s only requirements.
A platform for synthesis, with further work ahead
The experiment shows a way to connect electrochemical carbon conversion with the selectivity of enzymes. It does not yet demonstrate cost-competitive food manufacture, a reduction in agricultural land use or net carbon removal over a complete life cycle.
Those outcomes depend on scale, the source of electricity and carbon dioxide, reagent production, enzyme durability and purification. The presence of formaldehyde as an intermediate also underlines why process control and product-quality testing matter.
For another example of how changing an enzyme alters a useful chemical reaction, see our coverage of redesigned peroxygenases.
Source
Liu, G. et al. (2024). Solar-driven sugar production directly from CO2 via a customizable electrocatalytic–biocatalytic flow system. Nature Communications, 15, 2636. Read the study.
Update note: The original publication date and URL are retained. This revision specifies the sugar produced, qualifies the efficiency comparison and identifies the additional reducing-agent requirement.
