Researchers Watch Photosynthesis Catalyst In Action
February 15, 2013

Scientists Use X-Ray Laser To Watch Photosynthesis In Action

Lee Rannals for - Your Universe Online

Researchers at Stanford University and the Department of Energy's (DOE) SLAC National Accelerator Laboratory used an X-ray laser to get a glimpse of photosynthesis in action. Using the laser, they were able to look at the structure and chemical behavior of a natural catalyst involved in photosynthesis.

"This method opens up the way to study changes going on in the catalytic cycle of the water oxidation in nature," Junko Yano, a chemist at Lawrence Berkeley National Laboratory and co-researcher in the experiment, told redOrbit. "Understanding the water oxidation reaction in nature would help us developing artificial photosynthetic devices based on the design concept of the natural system."

A report of the team´s work appeared recently in the journal Science and is considered a breakthrough study for understanding atomic-scale transformations in photosynthesis and other biological and industrial processes that depend on catalysts.

"All life that depends on oxygen is dependent on photosynthesis," said Yano. "If you can learn to do this as nature does it, you can apply the design principles to artificial systems, such as the creation of renewable energy sources. This is opening up the way to really learn a lot about changes going on in the catalytic cycle."

Synthetic catalysts have become vital to modern industrial processes like the production foods, pharmaceuticals and fertilizers. Naturally occurring catalysts have long served as an explanatory key and model for creating their synthetic counterparts.

The experiments performed by the team focused on Photosystem II, a protein complex found in plants, algae and some microbes that carries out the oxygen-producing stage of photosynthesis. This process takes place with the help of a simple catalyst.

Photosystem II absorbs a photon of sunlight and releases a proton and an electron in each step, providing the energy to link two water molecules, break them apart, and release a molecule of oxygen.

Previous research froze crystals of the catalyst at various stages of the processes in order to study its shape and structure during each phase. However, researchers wanted to watch this biochemical process unfurl in front of them, and the LCLS X-ray laser helped make that possible.

"We decided to use two X-ray techniques at once at the LCLS: crystallography to look at the overall atomic structure of Photosystem II, and spectroscopy to document the position and flow of electrons in the catalyst," said Vittal Yachandra, a Berkeley Lab chemist and co-leader of the project. "The electrons are important because they are involved in making and breaking bonds and other processes at the heart of chemical reactions."

Physicist Uwe Bergmann of Stanford University´s SLAC National Accelerator Laboratory says the team´s results represent a critical step towards the ultimate goal of watching the full cycle of the splitting of water into oxygen during photosynthesis. He said that using both techniques also verified that the molecular structures of the samples were not damaged during measurement with the LCLS.

"It's the first time that we have resolved the structure of Photosystem II under conditions in which we know for sure that the machinery that does the water splitting is fully intact," Bergmann said. The team hopes to study all the steps carried out by Photosystem II in higher resolution for future experiments. This could reveal the full transformation of water molecules into oxygen molecules.

"Getting a few of the critical snapshots of this transition would be the final goal," said Jan Kern, a chemist who holds a joint position at Berkeley Lab and SLAC, and is the first author of the paper. "It would really answer all of the questions we have at the moment about how this mechanism works."

At the start of the year, researchers from Ludwig Maximilians Universitat (LMU) found what scientists considered to be the missing link in photosynthesis. Ultimately, this finding could help scientists improve photosynthetic performance by replacing or modifying specific components of the electron transport chain.