14 DAY TRIAL // When various organisms and plants first began conducting photosynthesis, the process did not result in the production of oxygen (anoxygenic photosynthesis). However, in time, a switch occurred, which enabled the emergence of an oxygenic (oxygen-production) version of the process. A team of experts now analyzes how this happened.
Photosynthesis is indeed one of the most fundamental processes that allowed for the development of life here on Earth. Its main role is to help plants and certain organisms convert carbon dioxide and water into oxygen and energy, using sunlight as a catalyst.
But the process was not always set up like this. There was a time in Earth's distant history when it did not result in the production of oxygen. After this changed, the critical element was finally allowed to accumulate in the atmosphere in large enough quantities to enable to development of complex life.
Without oxygenic photosynthesis, the emergence of complex lifeforms, including mammals and humans, wouldn't have been possible. Past studies have demonstrated a direct link between the size and complexity of organisms and the amount of oxygen in Earth's atmosphere at any given time.
While all these facts are known, what remains to be determined is how the switch from anoxygenic to oxygenic photosynthesis occurred. A new paper, entitled “Light-driven oxygen production from superoxide by manganese-binding bacterial reaction centers,” explores this question.
The paper is authored by investigators James Allen, JoAnn Williams, Tien Le Olson, Aaron Tufts, Paul Oyala and Wei-Jen Lee, who are all based at the Arizona State University (ASU) College of Liberal Arts and Sciences' Department of Chemistry and Biochemistry.
One of the main conclusions of the study was that the switch did not occur at once. In other words, the system evolved from one stage to the other through a series of intermediary steps, all of which depended on the emergence of a single molecule, a protein outfitted with a manganese-calcium cluster.
“In photosynthesis, the oxygen is produced at a special metal site containing four manganese and one calcium atom connected together as a metal cluster. This cluster is bound to the protein called photosystem II that provides a carefully controlled environment for the cluster,” Allen explains.
Photosystem I and photosystem II are two pigment-protein complexes that play a critical role in oxygenic photosynthesis. Whenever they are hit by photons, they promote the breaking of two water molecules into molecular oxygen (O2) and four protons (hydrogen atom nuclei).
The paper covers how a manganese-calcium cluster may have helped the early, anoxygenic version of photosynthesis develop into a more complex form.