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UC Irvine team discovers nitrogenase Fe protein can reduce CO2 to CO; implications for biofuel production

A team at the University of California, Irvine has discovered that the iron protein (the reductase component) of the natural enzyme nitrogenase can, independent of its natural catalytic partner, convert CO2 to carbon monoxide (CO)—a syngas used to produce useful biofuels and other chemical products.

The team, led by Professor Yilin Hu (Molecular Biology and Biochemistry), also found that they could express the reductase component alone in the soil bacterium Azotobacter vinelandii to convert CO2 in a manner more applicable to large-scale production of CO. This whole-cell system could be explored further for new ways of recycling atmospheric CO2 into biofuels and other commercial chemical products. A paper on their work is published in the journal Nature Chemical Biology.

Nitrogenase is a key enzyme in the global nitrogen cycle, and is responsible for the reduction of nitrogen (N2) to ammonia (NH3). The iron (Fe) protein is the reductase component of nitrogenase; a reductase is an enzyme that promotes the chemical reduction of a substance.

In nature, during substrate turnover, the Fe protein forms a functional complex with its catalytic partner, permitting ATP-dependent transfer of electrons from the former to the latter and the subsequent reduction of substrates at the cofactor site of the catalytic component upon accumulation of a sufficient number of electrons.

Such a two-component catalytic system enables two reactions under ambient conditions that are important for energy- and environment-related areas: (i) the reduction of nitrogen (N2) to ammonia (NH3); and (ii) the reduction of carbon monoxide (CO) or carbon dioxide (CO2) to hydrocarbons. Meanwhile, questions have arisen as to whether the actions of Fe proteins can occur in the absence of their respective catalytic partners and what interesting chemistry can be performed by these unique reductases on their own.

To address these questions, we examined the ability of Fe proteins to reduce CO2 in vitro independent of their catalytic partners.

—Rebelein et al.

The researchers said that the ability of the Fe protein to effect ambient CO2 reduction opens up new avenues to understand and improve the process of CO2 conversion. Further, the engineered A. vinelandii—a non-carboxydotrophic organism—may offer a possible biotechnological advantage in whole-cell production of syngas CO, as carboxydotrophic organisms predominantly convert CO2 and CO for use in producing their own energy and biomass instead of releasing CO as an unwanted product.

Furthermore, the reaction of CO2 reduction by Fe proteins could be coupled with the reaction of CO reduction by complete nitrogenase systems, which may prove instrumental in developing strategies for sequestration of CO2 concomitant with the conversion of this greenhouse gas into valuable chemical products.

—Rebelein et al.

Resources

  • Johannes G Rebelein, Martin T Stiebritz, Chi Chung Lee & Yilin Hu (2016) “Activation and reduction of carbon dioxide by nitrogenase iron proteins” Nature Chemical Biology doi: 10.1038/nchembio.2245

Comments

SJC

This could be BIG, with reverse gas shift you have to give up an H2.

sd

OK, but the article is not clear on where the energy comes from. Sun light or solar energy? You can not reduce CO2 without an input of energy.

SJC

The idea is to use LESS energy, that is what this does.

gorr

Christmas was 3 days ago and i didn't get my ultra cheap synthetic gasoline for sale near where i live that im asking for since many years.

Trees

We're currently within a chemical/biological revolution spurred by the need for better understanding of nature's activities (GW). For example when evaluating soil for carbon sequestration and conversion of CO2. Not to many years ago the scientist had no idea that soil played such a large part. The nitrogen cycle is still under study. The article above is depicting a new frontier for enzymes within a cell system that could convert CO2 directly to fuel. These natural biological systems are common within our environment and just know a slightly better understanding of how they work.

By the way "fuel" is not a bad energy source. It's a remarkable battery of energy. Same for the ICE, it's not inherently evil. Our scientist and engineers are just now working on improving these systems. It's a mistake to declare or make assumptions, at least upon the energy sector, "coal is dirty, wind is free".

sd

SJC: When you oxidize Carbon to form CO2 (burning coal for example), you get energy out. To convert CO2 back to carbon you have to put energy back and as none of the processes run at 100% efficient, you need to put in more energy than you got out. Generally speaking, a catalyst will allow the reaction to run with less wasted energy but you still need to put in more energy than you got out. If you do not understand this, read up on the laws of thermodynamics. I was asking where the energy came from. You could be getting energy from transforming the iron to iron oxide but then you need to put energy back to reduce the iron oxide back to iron.

As an interesting side note, my company used to run a CNC plasma cutter with a water table (it has since been replaced with a fiber laser) Periodically, we would have to clean out the bottom of the water tank which contained scrap and what was essentially iron shot. When we would dump to barrels of the wet waste into a larger container for recycling, the workers commented that it stank. I recognized that the odor was ammonia as the iron was stripping the O from H20 to form iron oxide and the freed hydrogen was combining with nitrogen in the air to form ammonia. The iron also acts as a catalyst for this reaction. There was also some white crystals being formed which might have been ammonium nitrate but I did not try to test this hypothesis:)

SJC

sd,
"If you do not understand this, read up on the laws of thermodynamics"
No need to be snarky, I know thermodynamics.
It uses less energy and is thus more efficient.
If you continue to insult you will be reported.

Dr. Strange Love

What about Iron Bacteria? Our well water has iron and manganese as is typical. Since we have a small amount of iron, our Torpedo-sized water softener is able to filter most of the iron out (higher amounts require a Iron berm filter as well). Iron Bactria lives everywhere. Once or twice a year we need to add Bleach to brine tank to kill the iron bacteria living in the Resin in the filter. The Iron bacteria will start to release excess Sulfur over time, hence the Rotten Egg smell.

Dr. Strange Love

Btw. The team isolated the Iron baring protein from the Nitrogenase base. This is really all that we know for sure. It is highly likely that this protein is where the CO2 to CO reduction occurs. I don't believe the bacteria that harnesses this protein uses sunlight to facilitate the Electron redox exchange. I believe the ATP cellular process provides this.

Dr. Strange Love

They also need more money to do in Vivo Genetic modifications on the bacteria to over-express the CO product without killing the creature. Another funding project will be to do in Vitro research on the Components (the iron protein is one) of the entire Nitrogenase to explore processes that would render CO etc. from Sunlight.

sd

SJC: My comment was not intended to be a snarky answer. I had asked a legitimate question on where the energy came from as the article was not clear on that point and I get back from you what might be considered a snarky answer that it uses less energy. OK, but what is the source of the energy?

Alain

As distributed renewable H2 production will become convenient and cheap owing to H2 fuel cell cars, biological means to combine H2 and CO2 to biomass opens fantastic possibilities.
Proteins, complex chemicals, polymers, ... can be made out of water and air.

All the materials and food we want to consume only comprise a fraction of the energy we currently need for fuel, heating and electricity.

Once our "conventional" energy can be produced green, we can can also produce all the chemicals, polymers, proteins, starches and lipids by virtue of this biotech.

And meanwhile the H2 production stabilizes the electricity grid.

Importantly, these biochemical catalists don't need rare resources, don't produce any wast, are fully recyclable, and can be upscaled very fast. Compare that with conventional catalyst!

Also, because the "food" for the organisms is sterile gases, it's much easier to prevent contamination of the bioreactor.

Great step forward.

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