Researchers at SLAC National Accelerator Laboratory and Lawrence Berkeley National Laboratory (together with collaborators in Sweden, Germany and the UK) shed new light In the last step of photosynthesis. They observed in atomic detail how Photosystem II, a protein complex found in plants, undergoes a transformation that results in the loss of an extra oxygen atom. Scientists believe the discoveries will help provide a roadmap for improving clean energy sources. “It will really change the way we think about System Two,” said Uwe Bergmann, a scientist and professor at the University of Wisconsin-Madison, who co-authored the paper.
The researchers took “ultra-high-resolution images” of different stages of the process (at room temperature), giving them new insight into exactly how and where oxygen is produced. Baseball can offer a simple (if somewhat forced) metaphor to illustrate the process. “The center goes through four stable oxidation states, defined as S0 through S3, when exposed to sunlight,” SLAC explains. “On a baseball field, S0 will be the starter of the game when the player in the home is ready to bat. S1-S3 will be players on first, second, and third.” Based on this metaphor, the batter contacting the forward runners indicates that the batter absorbs a photon of sunlight. “When the fourth ball is hit, the player slides home, scoring a run or, in the case of the second picture system, releasing one molecule of breathable oxygen.” It’s that last stage (S4, between the third base and the sliding house in our metaphor) that they first depicted, where two oxygen atoms bond to release an oxygen molecule, revealing additional steps we haven’t seen before.
The video below demonstrates the team’s process and discoveries.
“Most of the processes that produce respirable oxygen occur in this last step,” said Vital Yachandra, a Berkeley Lab scientist and co-author of the paper. Posted in nature. “But there are many things going on in different parts of the second picture system and they must all eventually come together for the reaction to be successful. Just like in baseball, factors such as the position of the ball and the position of the baseman and fielders influence the movements the player takes to reach To home base, the environment of the protein around the catalytic center affects how this interaction occurs.”
The researchers expect to upgrade the X-rays later this year to shed more light on the process. It will use a repetition rate of 1 million beats per second, up from the 120 beats per second used in this experiment. “With these upgrades, we will be able to collect several days’ worth of data in just a few hours,” Bergman said. “We will also be able to use soft X-rays to further understand the chemical changes that occur in the system. These new capabilities will continue to drive this research forward and shed new light on the process of photosynthesis.”
The team believes the findings will help them “develop artificial photosynthetic systems that mimic photosynthesis to harvest natural sunlight to convert carbon dioxide into hydrogen and carbon-based fuels.” Jean Kern, co-author and another Berkley Lab scientist, said, “The more we know about how nature does this, the closer we get to using these principles in human-made processes, including ideas of artificial photosynthesis as a clean and sustainable energy source.”
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