Researchers at SLAC National Accelerator Laboratory and Lawrence Berkeley National Laboratory (along with collaborators in Sweden, Germany and the UK) have shed new light on the final step of photosynthesis. They observed in atomic detail how Photosystem II, a protein complex found in plants, undergoes a transformation that leads to the loss of an extra oxygen atom. The scientists believe the discoveries will help provide a roadmap for optimizing 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 researchers took “extremely high-resolution images” of different stages of the process (at room temperature), giving them a new perspective on how and where oxygen is produced. Baseball can provide a simple (if somewhat forced) metaphor to illustrate the process. “The core goes through four stable oxidation states, known as S0 to S3, when exposed to sunlight,” explains SLAC. “On a baseball field, S0 would be the start of the game when a player on base is ready to hit. S1-S3 would be players in first, second and third”. According to this metaphor, a batter making contact to advance runners means that the complex absorbs a photon of sunlight. “When the fourth ball is hit, the player slides toward home plate, scoring a run or, in the case of Photosystem II, releasing a breathable oxygen molecule.” It’s that final stage (S4, between third base and the slide home in our metaphor) that they first photographed, where two oxygen atoms come together to release an oxygen molecule, revealing additional steps never seen before.
The following video illustrates the process and the team’s findings.
“Most of the process that produces breathable oxygen occurs in this last step,” said Vittal Yachandra, a Berkeley Lab scientist and co-author of the paper, published in Nature. “But there are several things happening in different parts of Photosystem II and they all have to come together at the end for the reaction to succeed. Just as in baseball, factors such as the location of the ball and the position of the basemen and outfielders affect the movements a player makes to get on base, the protein environment around the catalytic center influences how this reaction develops. reaction”.
The researchers expect an X-ray update later this year to shed more light on the process. It will use a repetition rate of up to one million pulses per second, versus the 120 per second used in this experiment. “With these updates, we will be able to collect multi-day data in just a few hours,” Bergmann said. “We will also be able to use soft X-rays to better understand the chemical changes that occur in the system. These new capabilities will continue to drive this research forward and shed new light on photosynthesis.”
The team believe the results will help them “develop artificial photosynthetic systems that mimic photosynthesis to harvest natural sunlight to convert carbon dioxide into hydrogen and carbon-based fuels.” Jan Kern, another co-author and a Berkley Lab scientist, said: “The more we learn about how nature does it, the closer we come to using those same principles in man-made processes, including ideas for artificial photosynthesis as a method clean and efficient.” sustainable energy source.
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