a machine that scientists could previously only operate blindly
Beneath every breath of air and every harvest lies a hidden chemistry performed by bacteria, governed by enzymes whose inner workings have long eluded human sight. An international team from the United Kingdom, Argentina, and Japan has now mapped, atom by atom, the precise sequence of events inside a copper enzyme called CuNiR — the molecular machine responsible for a critical step in Earth's nitrogen cycle. Using ultrafast X-ray pulses at Japan's SACLA facility, they resolved a decades-old question about the order in which molecules arrive at the enzyme's active site, producing what amounts to an instruction manual for a process that sustains all life on land.
- For decades, radiation from conventional X-ray sources chemically corrupted enzyme samples mid-measurement, leaving the inner workings of CuNiR permanently obscured — a problem that stalled the entire field.
- An international collaboration fired X-ray pulses lasting less than ten femtoseconds, moving faster than radiation damage itself and capturing atomic snapshots with hundredths-of-an-Angström precision across dozens of frozen enzyme crystals.
- The team discovered that nitrite binds to the enzyme's copper center before the electron arrives — a 'top-hat' configuration that settles a foundational dispute about the reaction's sequence and opens the door to deliberate molecular engineering.
- Slower electron transfer in certain bacterial species gave researchers a rare window into fleeting intermediate states, turning a biological limitation into an experimental advantage.
- The findings now point toward designing enzyme inhibitors and modifications that could reduce greenhouse gas emissions, curb nitrogen pollution in waterways, and refine agricultural and medical applications — though replicating the results at room temperature remains the field's next critical challenge.
Nitrogen fills the atmosphere and runs through every living cell, yet plants and animals cannot use it without bacterial intermediaries. One copper enzyme, CuNiR, performs a pivotal step in this cycle — converting nitrite into nitric oxide — but for years it functioned as a black box. Scientists knew what it did; they could not see how.
A team spanning the United Kingdom, Argentina, and Japan set out to change that. Felix Ferroni of Argentina's Conicet and the National University of Litoral collaborated with researchers from the University of Liverpool and Japan's RIKEN SPring-8 center. Their findings, published in Nature Communications, mapped the enzyme's structure across multiple functional states at atomic resolution — a first for this system.
The core question was deceptively simple: does nitrite reach the enzyme's active site before or after the electron? Earlier attempts had failed because conventional X-ray sources triggered photoreduction, chemically altering the enzyme during measurement and corrupting results. The team circumvented this by using an ultrafast X-ray laser at Japan's SACLA facility, firing pulses shorter than ten femtoseconds — fast enough to capture an image before radiation could cause harm. Dozens of enzyme crystals from three bacterial species, cooled to 196 degrees below zero Celsius, were measured with precision reaching hundredths of an Angström.
The answer was clear: nitrite arrives first. It displaces water molecules at the active site while preserving a five-point anchoring geometry around the copper atom — a shape the researchers described as 'top-hat' — before the electron follows. Slower electron transfer in certain bacterial species allowed the team to record intermediate states that faster enzymes pass through too quickly to observe.
Ferroni described the discovery as an instruction manual for a machine scientists had previously operated blind. Knowing the reaction's sequence makes it possible to design inhibitors or engineer modifications with uses in agriculture, medicine, and environmental monitoring. The team acknowledged that cryogenic conditions may not perfectly mirror what happens in living soil, and capturing images at room temperature remains the next frontier. If that challenge is met, the method could extend to other metal-containing enzymes — and the practical stakes are considerable, from curbing greenhouse gas emissions to reducing the nitrogen runoff that contaminates rivers and groundwater worldwide.
Nitrogen is everywhere—in the air, in soil, in every living thing—but plants and animals cannot use it directly. They depend on bacteria to convert it into usable forms, and then to return it to the atmosphere or ground. For decades, scientists knew that a copper enzyme called CuNiR performed a crucial step in this cycle, transforming nitrite into nitric oxide. But they could not see how it worked at the atomic level. The enzyme remained a black box.
That changed when researchers from the United Kingdom, Argentina, and Japan joined forces to solve the problem. Felix Ferroni, a biotechnology graduate and independent researcher at Argentina's Conicet and the National University of Litoral, worked alongside Samuel Rose, Svetlana Antonyuk, and Samar Hasnain from the University of Liverpool, and Masaki Yamamoto and Takehiko Tosha from Japan's RIKEN SPring-8 center and University of Hyogo. Their results, published in Nature Communications, revealed the enzyme's structure atom by atom across multiple functional states—something never before achieved for this particular system.
The central mystery was simple but profound: does nitrite arrive at the enzyme's active site before or after the electron? Previous attempts to answer this question had failed because conventional X-ray sources altered the enzyme chemically during measurement, a phenomenon called photoreduction that corrupted the data. The international team bypassed this obstacle by using an ultrafast X-ray laser at Japan's SACLA facility. This device fires pulses lasting less than ten femtoseconds—a femtosecond being a millionth of a billionth of a second—fast enough to capture an image before radiation could damage the sample. They prepared between 42 and 64 enzyme crystals from three bacterial species, cooled to 196 degrees Celsius below zero, and measured atomic distances with precision to hundredths of an Angström, a unit equal to one ten-millionth of a millimeter.
What they found resolved a question that had lingered for years. The enzyme's active site, at rest, contains two water molecules and three amino acids called histidines, forming five anchor points around copper. When nitrite arrives, it displaces the water but maintains the five-point geometry by binding at two ends simultaneously—a configuration the researchers called "top-hat" shaped. Crucially, this binding occurs before the electron arrives. In the reduced state, after the electron has been received, the water molecules vanish and only three anchor points remain, with a different amino acid filling the gap. The slower electron transfer in some bacterial species allowed the team to capture intermediate states that occur too rapidly in faster enzymes to be recorded.
Ferroni explained the significance to Infobea: knowing that nitrite arrives before the electron allows precise control of the reaction, opening doors to designing enzyme inhibitors or modifications with applications in agriculture, medicine, and environmental monitoring. The research functions as an instruction manual for a machine that scientists could previously only operate blindly. Yet the team acknowledged limitations. Working at cryogenic temperatures may not reflect what actually happens in soil, where temperature and molecular movement differ vastly. The next step would be to capture images at room temperature, though radiation damage would increase and require careful study. If that challenge is solved, the same method could be applied to other metal-containing enzymes, potentially revolutionizing how scientists understand catalysis at the molecular level. The implications extend beyond basic science: better understanding of this enzyme could help reduce greenhouse gas emissions and improve nitrogen use in agriculture, where excess nitrogen contaminates groundwater and rivers.
Notable Quotes
We captured something like a short film of the enzyme atom by atom in several functional states, something never before achieved for this particular system— Felix Ferroni, independent researcher at Argentina's Conicet and National University of Litoral
Knowing that nitrite arrives before the electron allows precise control of the reaction, opening doors to designing enzyme inhibitors or modifications with applications in agriculture, medicine, and environmental monitoring— Felix Ferroni
The Hearth Conversation Another angle on the story
Why does it matter that we now know nitrite arrives before the electron? Couldn't we have just guessed?
Because guessing leads to failed experiments and wasted resources. Knowing the sequence lets us design inhibitors or speed up the reaction deliberately. It's the difference between knowing a recipe and knowing why each ingredient matters.
But you had to freeze the enzyme to 196 degrees below zero. Doesn't that make the whole thing artificial?
It does, which is why the team is already planning room-temperature studies. But freezing was the only way to prevent radiation from destroying the sample during imaging. It's a trade-off—you lose some realism to gain clarity.
What happens if they succeed at room temperature?
Then the same technique could be applied to hundreds of other metal-containing enzymes. You'd have a universal tool for seeing how catalysis actually works inside cells.
And the practical applications? Is this just for scientists, or does it affect real life?
Both. In agriculture, it could help us use nitrogen more efficiently so it doesn't poison rivers. In medicine, it could lead to new drugs. In industry, it could help treat wastewater. The basic science opens all those doors at once.
So this is one of those discoveries that seems abstract until suddenly it's not.
Exactly. A decade from now, something you use every day might exist because someone spent years staring at an enzyme's atomic structure.