Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Making the oxygen we breathe, a photosynthesis mechanism exposed

12.06.2018

Arguably, the greatest fueler of life on our planet is photosynthesis, but understanding its labyrinthine chemistry, powered by sunlight, is challenging. Researchers recently illuminated some new steps inside the molecular factory that makes the oxygen we breathe.

Though chlorophyll is the best-known part, for the vivid green it colors nature, many compounds work together in photosynthesis. And Georgia Tech chemists devised clever experiments to inspect players intimately involved in the release of O2 from water in what's known as photosystem II (PSII). 


A key O2 catalyst, the metal cluster in photosystem II, one of two O2 photosynthesis mechanisms. On top of it, a tyrosine molecule flips back and forth chemically and physically to speed up electron transfer in the oxygen-producing part of photosynthesis.

Credit: Georgia Tech / Brumfield / Barry Lab

PSII is a complex protein structure found in plants and algae. It has a counterpart called photosystem I, an equally complex light-powered producer of oxygen and biomaterials.

Some questions and answers below will help elucidate the researchers' findings about a small metal catalyst and an amino acid inside PSII that work hand-in-glove to produce O2.

"Photosynthesis in plants and algae can be compared to an artificial solar cell," said principal investigator Bridgette Barry, who is a professor in Georgia Tech's School of Chemistry and Biochemistry. "But, in photosynthesis, light energy fuels the production of food (carbohydrates) instead of charging a battery. O2 is released from water as a byproduct."

Barry, first author Zhanjun Guo, and researcher Jiayuan He published their research on May 11, 2018, in the journal Proceedings of the National Academy of Sciences. Their work was funded by the National Science Foundation.

How does photosynthesis II release oxygen from water?

Many details are still unknown, but here are some basic workings.

PS II is a biochemical complex made mostly of large amino acid corkscrew cylinders and some smaller such cylinders strung together with amino acid strands. The reaction cycle that extracts the O2 from H2O occurs at a tiny spot, which the study focused on.

For scale, if PSII were a fairly tall, very wide building, the spot might be the size of a large door in about the lower center of the building, and the metal cluster would be located there. Intertwined in the proteins would be sprawling molecules that include beta-carotene and chlorophyll, a great natural photoelectric semiconductor.

"Photons from sunlight bombard photosystem II and displace electrons in the chlorophyll," Barry said. "That creates moving negative charges."

What is the metal catalyst?

The metal catalyst acts like a capacitor, building up charge that it uses to expedite four chemical reactions that release the O2 by removing four electrons, one-by-one, from two water molecules. In the process, water also spins off four H+ ions, i.e. protons, from two H2O molecules.

An additional highly reactive compound acts as a "switch" to drive the electron movement in each step of the reaction cycle.

What's the 'switch,' and what does it do?

This is where the new study's insights come in.

Near the metal cluster is a common amino acid called tyrosine, a little building block on that mammoth protein building. The light reactions remove one electron from tyrosine, making it what's called an unstable radical, and the radical version of tyrosine strongly attracts a new electron.

It very quickly gets that new electron from the metal cluster. As PSII absorbs photons, the taking of an electron from tyrosine and its radical's grabbing of a new one from the cluster repeats rapidly, making the tyrosine a kind of flickering switch.

"The tyrosine radical drives the cycle around, and what they (Guo and He) did in the lab was to develop a way of seeing the radical reaction in the presence of the metal cluster," Barry said.

Guo and He also found that the calcium atom in the cluster has key interactions with tyrosine.

How did they observe that single chemical component in a living system?

Figuring out how to make the reactions observable was painstaking. The researchers isolated some PSII from spinach, and they slowed it way down by cooling it in the dark.

Then they gave it a burst of red light to prepare one step in the reaction cycle, then a green flash to take the electron from tyrosine. Then the electrons slowly returned to the tyrosine.

The researchers observed the processes via vibrational spectroscopy, which revealed qualities of tyrosine's chemical bonds. The researchers also examined the calcium and discovered a special interaction between it and tyrosine.

"A new thing we saw was that the calcium ion made the tyrosine twist a certain way," Barry said. "It turns out that the tyrosine may be a very flexible switch."

The researchers also swapped out calcium for other metals and found that the calcium fulfills this role quite optimally.

So, why is understanding photosynthesis important?

"Oxygen photosynthesis really is the great fueler life on our planet," Barry said.

About two billion years ago, the photosynthesis that generates O2 exploded, and as breathable oxygen filled Earth's oceans and atmosphere, life began evolving into the complex variety we have today. There are also pragmatic reasons for studying photosynthesis.

"You could work with it to make crops more productive," Barry said. "We may have to repair and adapt the photosynthesis process someday, too."

Environmental stresses could possibly weaken photosynthesis in the future, calling for biochemical tweaks. Also, natural photosynthesis is an exceptionally good model for photoelectric semiconductors like those used in emerging energy systems.

###

The research was funded by the National Science Foundation (grant MCB-14-11734). Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect views of the National Science Foundation.

Media Contact

Ben Brumfield
ben.brumfield@comm.gatech.edu
404-660-1408

 @GeorgiaTech

http://www.gatech.edu 

Ben Brumfield | EurekAlert!
Further information:
http://www.rh.gatech.edu/news/606884/making-oxygen-we-breathe-photosynthesis-mechanism-exposed
http://dx.doi.org/10.1073/pnas.1800758115

Further reports about: Electrons H2O Photosynthesis amino acid biochemical chemical bonds tyrosine

More articles from Life Sciences:

nachricht Developing a digital holography-based multimodal imaging system to visualize living cells
03.06.2020 | Kobe University

nachricht Possible physical trace of short-term memory found
03.06.2020 | Institute of Science and Technology Austria

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: K-State study reveals asymmetry in spin directions of galaxies

Research also suggests the early universe could have been spinning

An analysis of more than 200,000 spiral galaxies has revealed unexpected links between spin directions of galaxies, and the structure formed by these links...

Im Focus: New measurement exacerbates old problem

Two prominent X-ray emission lines of highly charged iron have puzzled astrophysicists for decades: their measured and calculated brightness ratios always disagree. This hinders good determinations of plasma temperatures and densities. New, careful high-precision measurements, together with top-level calculations now exclude all hitherto proposed explanations for this discrepancy, and thus deepen the problem.

Hot astrophysical plasmas fill the intergalactic space, and brightly shine in stellar coronae, active galactic nuclei, and supernova remnants. They contain...

Im Focus: Biotechnology: Triggered by light, a novel way to switch on an enzyme

In living cells, enzymes drive biochemical metabolic processes enabling reactions to take place efficiently. It is this very ability which allows them to be used as catalysts in biotechnology, for example to create chemical products such as pharmaceutics. Researchers now identified an enzyme that, when illuminated with blue light, becomes catalytically active and initiates a reaction that was previously unknown in enzymatics. The study was published in "Nature Communications".

Enzymes: they are the central drivers for biochemical metabolic processes in every living cell, enabling reactions to take place efficiently. It is this very...

Im Focus: New double-contrast technique picks up small tumors on MRI

Early detection of tumors is extremely important in treating cancer. A new technique developed by researchers at the University of California, Davis offers a significant advance in using magnetic resonance imaging to pick out even very small tumors from normal tissue. The work is published May 25 in the journal Nature Nanotechnology.

researchers at the University of California, Davis offers a significant advance in using magnetic resonance imaging to pick out even very small tumors from...

Im Focus: I-call - When microimplants communicate with each other / Innovation driver digitization - "Smart Health“

Microelectronics as a key technology enables numerous innovations in the field of intelligent medical technology. The Fraunhofer Institute for Biomedical Engineering IBMT coordinates the BMBF cooperative project "I-call" realizing the first electronic system for ultrasound-based, safe and interference-resistant data transmission between implants in the human body.

When microelectronic systems are used for medical applications, they have to meet high requirements in terms of biocompatibility, reliability, energy...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Dresden Nexus Conference 2020: Same Time, Virtual Format, Registration Opened

19.05.2020 | Event News

Aachen Machine Tool Colloquium AWK'21 will take place on June 10 and 11, 2021

07.04.2020 | Event News

International Coral Reef Symposium in Bremen Postponed by a Year

06.04.2020 | Event News

 
Latest News

An MRI technique has been developed to improve the detection of tumors

03.06.2020 | Medical Engineering

K-State study reveals asymmetry in spin directions of galaxies

03.06.2020 | Physics and Astronomy

The cascade to criticality

03.06.2020 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>