A team of researchers at the SLAC National Accelerator Laboratory and Lawrence Berkeley National Laboratory, along with collaborators in Sweden, Germany, and the UK, has made significant progress in understanding the final step of photosynthesis. Using “extremely high-resolution images” taken at room temperature, they were able to observe the transformation of Photosystem II, a protein complex found in plants, that results in the loss of an extra oxygen atom.
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The researchers believe that their discoveries will help pave the way for developing clean energy sources. “It’s really going to change the way we think about Photosystem II,” said Uwe Bergmann, a scientist and professor at the University of Wisconsin-Madison, who co-authored the paper.
The team took multiple high-resolution images of different stages of the process and identified how and where oxygen is produced. To illustrate the process, the team used a baseball metaphor, explaining that “the centre cycles through four stable oxidation states, known as S0 through S3, when exposed to sunlight.” When the “fourth ball is hit,” the player slides into home, and “in the case of Photosystem II, one molecule of breathable oxygen” is released. The team imaged the final stage, S4, for the first time, which revealed previously unseen additional steps in which two oxygen atoms bond to release an oxygen molecule.
Vittal Yachandra, a scientist at Berkeley Lab and co-author of the paper, said, “Most of the process that produces breathable oxygen happens in this last step.” However, he explained that there are several factors that affect how the reaction plays out, just like in baseball, where the position of the ball and the players affect how a player takes moves to get to home base.
The team plans to upgrade their X-ray technology later this year to obtain even more data on the process. They expect to be able to collect several days’ worth of data in just a few hours, and they will be able to use soft X-rays to further understand the chemical changes happening in the system.
The researchers believe that their findings will help them develop artificial photosynthetic systems that can mimic photosynthesis to convert carbon dioxide into hydrogen and carbon-based fuels. Jan Kern, another co-author and scientist at Berkley Lab, said, “The more we learn about how nature does it, the closer we get to using those same principles in human-made processes, including ideas for artificial photosynthesis as a clean and sustainable energy source.”
