Scientists working at the Department of Energy’s SLAC National Accelerator Laboratory have taken an important step towards understanding how nature makes plant food from nitrogen.

For now feeding and fueling humanity uses synthesized ammonia in NH3 form by a process that requires high temperatures and pressures that consumes an estimated 1.5 percent of the world’s energy use.

The SLAC team has identified a key atom that researchers have sought for more than a decade.  The atom lies at the heart of the crucial enzyme called nitrogenase.    Nitrogenase is the primary natural key in converting nitrogen in the air into a form that living things can use.

Scientists have long sought to determine the structure of this enzyme; because the hope to eventually reverse-engineer it and mimic nature’s gentle version of the reaction.

Chemist Serena DeBeer of Cornell University and the Max Planck Institute for Bioinorganic Chemistry, who led the team that performed crucial experiments at SLAC said in the press release, “The fascination with this enzyme is the fact that it enables this reaction to take place at room temperature and atmospheric pressure.”

Nitrogenanse Research Team Members. Click image for more info.

The race has been close to identifying the mystery atom.  It ended in a photo finish, in the Nov. 18 issue of Science, two independent teams; using different approaches, identified the atom as carbon.

The carbon atom has eluded scientists because of its sequestered location inside a cluster of metal atoms. The key in the SLAC’s team’s research was a technique called X-ray emission spectroscopy, or XES, which co-author Uwe Bergmann of SLAC had developed over the past decade.

FeMoco and P-Nitrogenase Model Per the Study. Click image for more info.

The SlAC team needed a trick to find the one important carbon inside the metal cluster. They used an intense beam of X-rays from the Stanford Synchrotron Radiation Lightsource to knock the innermost electrons out of iron atoms in the cluster. Normally other electrons from iron would fill this hole; but there was a tiny chance, much less than one in a thousand, that the hole would be filled by an electron belonging to a neighboring atom, and thus emit X-rays characteristic of the neighbor’s identity. It was this subtle feature in the X-ray emission spectrum that revealed that a carbon atom, rather than a nitrogen or oxygen, was bound to the iron atoms in the cluster.

Bergmann said, “This was a simple but important question and we were able to give a straightforward answer. I think this will have a big impact not only on the understanding of nitrogenase but on the use of X-ray emission spectroscopy.”

It is critically important to understand this as the preparation of food and fuel supplies in quantities for people numbering in the billions with high living standards in mind is a huge production, logistical and economic challenge.

The cluster of metal atoms is where nitrogen molecules from the air, the N2, are broken down and recombined to ammonia and other compounds by microbes in the soil. Then plants can take it up and spread it through the food chain.

It’s how we get roughly half of the nitrogen into the food supply for our bodies; the rest comes from artificial fertilizers primarily made via the Haber-Bosch reaction, the resource-intensive method widely used to convert atmospheric nitrogen to NU3 ammonia using air and natural gas for the hydrogen supply and heat for the process.

Researchers knew a decade ago that the central atom in the metal cluster must be nitrogen, oxygen or carbon. Each would affect the reaction differently. But how to identify this atom among the 20,545 total carbon atoms, 11,026 oxygen atoms and 5,431 nitrogen atoms in a very complex enzyme?

The perspective offered by the press release comes from a third party – chemist Brian Hoffman of Northwestern University, who has investigated nitrogenase for 30 years but was not involved in these studies saying, “Because it’s sequestered in the middle of a bunch of metal atoms and you’ve got no way to get your hands on it, it’s a really hard problem. What the team has done would appear to be a classic case where new technology leads to new science.”

So it is.  Note again quantities of the list of atoms of the three main elements in the nitrogenase enzyme. And that’s not including those metals mentioned.

It’s going to take a lot of science to synthesize that enzyme.  But when it’s done, the size of the market and the potential to the world’s economy will open a new door to one of the largest markets in history.


1 Comment so far

  1. jpstraley on November 21, 2011 9:21 AM

    Why not just introduce the trait into the target organism? Let corn make its own N , and avoid all that industrial infrastructure.

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