Paper details previously unknown step in process of converting light energy to chemical energy:
Photosynthesis – the process by which plants and some other organisms convert sunlight to food – is complex, and scientists don't fully understand how it works. But a team of researchers led by the US Department of Energy's SLAC National Accelerator Laboratory reckon they're closer to solving the mystery – they captured an image of the atoms inside cyanobacteria undergoing photosynthesis just as the tiny organism released oxygen.
X-ray lasers at SLAC's Linac Coherent Light Source at Stanford University, and the SPring-8 Angstrom Compact free electron LAser (SACLA) at a synchrotron radiation facility in Japan's SPring-8 lab, were directed at a specific protein used to catalyze the chemical reaction. The protein complex, dubbed Photosystem II, is used by organisms like cyanobacteria or algae to photosynthesize.
Photosystem II carries a molecule, made up of four manganese (Mn) atoms and one calcium (Ca) atom connected by oxygen atoms, and splits a water molecule apart to release oxygen. The research team managed to image the different steps in the reaction, and discovered a previously unknown step in the process.
[...] Tens or even hundreds of thousands of these snapshots are required to see how the atoms move over time. Capturing them is a tedious process that constantly requires fresh cyanobacteria samples, since each one gets destroyed after being exposed to the powerful X-ray pulse. The experimental setup to facilitate the research took six years to build, as the authors explained in a study published by Nature on Wednesday.
"The reaction cycle in Photosystem II involves four main steps, each triggered by the absorption of one photon. In each of the steps at the site of action in Photosystem II, a group of four Mn atoms and one Ca atom acts like a battery that gets more and more charged with each step," they told us. After four photons have been absorbed, Photosystem II strips protons from water molecules and brings them close enough that a new chemical bond is forged between the oxygen molecules to produce gas.
"In this last step there are at least four different events happening and in this new study it was possible to visualize some of these events for the first time" they explained.
[...] The researchers remain committed to their research. "This is a unique capability in nature. We focus our research on this protein because of the exciting implications for clean energy production and sustainability, and because Photosystem II has produced essentially all of the oxygen in our atmosphere, enabling the evolution of complex lifeforms that depend on oxygen respiration. It has been doing this reaction, which profoundly shaped our planet, for more than three billion years."
Journal Reference:
Bhowmick, A., Hussein, R., Bogacz, I. et al. Structural evidence for intermediates during O2 formation in photosystem II [open]. Nature (2023). https://doi.org/10.1038/s41586-023-06038-z
