An enzyme that converts air into electricity

Many of the scientists, academics and researchers across the world have been persistently working on the development of the technologies required for the clean source of energy to save this planet from the devastating impacts of climate change. Recently a team of scientists have discovered a remarkably efficient enzyme that converts air into energy. It opens a new window of opportunity for harvesting unlimited clean energy. The scientific journal: Nature published an article depicting the research on 08 March/2023. It reveals that this enzyme uses the low amounts of the hydrogen in the atmosphere to create an electrical current. It paves the way to create devices that literally would be able to make energy from thin air.

The research team, led by Dr Rhys Grinter, Ashleigh Kropp, and Professor Chris Greening from the Monash University Biomedicine Discovery Institute in Melbourne, Australia, produced and analyzed a hydrogen-consuming enzyme from a common soil bacterium. Molecular modelling and simulations were performed by Oxford Biochemistry and Queens College undergraduate Jack Badley and postdoctoral research fellow Dr RuyuJiya, under the supervision of Dr.Syma Khalid, Professor of Computational Microbiology in the Department of Biochemistry, Oxford University.

What is the miracle enzyme that turns air into energy?
"Many bacteria use hydrogen from the atmosphere as an energy source in nutrient-poor environments. The researchers extracted the enzyme responsible for using atmospheric hydrogen from a bacterium called Mycobacterium smegmatis. They showed that this enzyme, called Huc, turns hydrogen gas into an electrical current. The enzyme is extraordinarily efficient and is able to consume hydrogen below atmospheric levels - as little as 0.00005% of the air we breathe. The chosen bacterium Mycobacterium smegmatis was discovered in 1884 in Austria by a doctor, Sigmund Lustgarten.  

Huc is a "natural battery" that produces a sustained electrical current from air or added hydrogen. The discovery of Huc has considerable potential to develop small air-powered devices, for example as an alternative to solar-powered devices.

Huc is a highly efficient oxygen-insensitive enzyme that couples oxidation of atmospheric H2 to the hydrogenation of the respiratory electron carrier menaquinone.

How did the researchers extract the enzyme Huc? 'The researchers used several cutting-edge methods to reveal the molecular blueprint of atmospheric hydrogen oxidation. They used advanced microscopy (cryo-EM) to determine its atomic structure and electrical pathways, pushing boundaries to produce the most resolved enzyme structure reported by this method to date. Electrochemistry was used to demonstrate the purified enzyme creates electricity at minute hydrogen concentrations. Molecular modelling and simulations were used to identify the specific regions of the protein which allow hydrogen gas to enter the active site of the protein where it is transformed, but prevent oxygen getting through.'
The bacteria that produce enzymes like Huc are common and can be grown in large quantities, meaning we have access to a sustainable source of the enzyme. Dr.Grinter says that a key objective for future work is to scale up Huc production. "Once we produce Huc in sufficient quantities, the sky is quite literally the limit for using it to produce clean energy."

How does Huc create electricity from hydrogen? Enzymes are substances produced by living organisms that accelerate or allow for certain chemical reactions, including those that generate energy. Huc creates electricity from hydrogen inside the bacterium Mycobacterium smegmatis.

After hydrogen binds to Huc, its electrons are transferred to an iron-sulphur cluster inside the enzyme. These clusters pass the electrons to a molecule of vitamin menquinone, which has also bound to the enzyme at another site. This transfer changes the menquinone into menaquinol, which travels to the membrane of the bacterium. There, it comes into contact with another enzyme which removes its electrons, turning it back into menquinone. These electrons then form an electric current at the membrane.

The researchers show how they can extract one of the enzymes responsible for this conversion reaction. They then used a new technique called cryogenic electron microscopy - which won its developers a Nobel Prize in 2017 - to determine the atomic structure of Huc. This technique involves cooling the sample to cryogenic temperatures ? below -238 �F (-150�C), and bombarding it with electrons. These pass through and are captured by a camera to produce an extremely high-resolution image. Specifically, Huc turns hydrogen into electrical energy, and cryogenic electron microscopy also helped scientists understand this process.The enzyme binds to hydrogen and enables its oxidation - a reaction where it loses electrons, before passing them on to the vitamin menaquinone, or K2. Menaquinone is then able to transfer electrons at the bacterium's membrane or other electrode, producing an electric current like a 'natural battery'.

What are the potential uses of the enzyme Huc?

According to the study the potential applications include the followings: 'Huc could be used as a sensor for hydrogen. Huc produces electrical current when hydrogen is present. When Huc is placed in an electrical circuit, this current can be measured to determine the hydrogen concentration.'

 "Huc could use the electrons from small amounts of hydrogen in air to perform chemical modifications needed in industrial chemical synthesis." 'Possibly the most interesting application of Huc is to power small electronic devices using air or low concentrations of hydrogen. It means the devices are powered by a super-clean and sustainable energy source.It can also help us understand how our planet works.

The amount of hydrogen present in air is so small, only a small amount of electricity could be extracted from it.However, if the devices were provided with more hydrogen, produced in the burgeoning hydrogen economy, Huc could produce significantly more power.

Grinter estimates that 60% to 80% of these bacteria could have enzymes like Huc, indicating a potential untapped wealth of electricity from biological sources. These bacteria present especially in nutrient-deprived soils, and are constantly absorbing hydrogen.

"They absorb 70 million tonnes of hydrogen every year, and this shapes the composition of our atmosphere, which makes this process important for modulating the climate. Understanding the biochemistry of this process may allow us to harness it to stabilise our climate in the future."

The outcome of the research brings a beacon of hope that one day we would be able to produce electricity from thin air - all thanks to the gift of nature with such bacteria living in dirt. It's a time to pool our talents together in innovation, development and implementation of the emerging technologies for the benefit and welfare of mankind.

The writer is a former Editor, Journal of the Institution of Engineers, Bangladesh and writes from England