Washington, Jan 11 (ANI): Researchers have identified an enzyme that likely was a key contributor to the unprecedented appearance and dramatic rise of molecular oxygen on Earth around 2.4 billion years ago.
"There is a consensus from earth scientists that about 2.4 billion years ago there was a big spike in oxygen on Earth," said University of Illinois crop sciences and Institute for Genomic Biology professor Gustavo Caetano-Anolles who led the new study.
They generally agree that this rise in oxygen, called the Great Oxygenation Event, was tied to the emergence of photosynthetic organisms.
"But the problem now comes with the following question. Oxygen is toxic, so why would a living organism generate oxygen? Something must have triggered this," he noted.
Caetano-Anolles and his colleagues looked for answers in the "molecular fossils" that still reside in living cells. They analysed protein folds in nearly a thousand organisms representing every domain of life to assemble a timeline of protein history.
Their timeline for this study was limited to single-fold proteins (which the researchers believe are the most ancient), and was calibrated using microbial fossils that appeared in the geologic record at specific dates.
The analysis revealed that the most ancient reaction of aerobic metabolism involved synthesis of pyridoxal (the active form of vitamin B6, which is essential to the activity of many protein enzymes) and occurred about 2.9 billion years ago.
An oxygen-generating enzyme, manganese catalase, appeared at the same time.
Catalases convert hydrogen peroxide to water and oxygen. The researchers hypothesize that primordial organisms "discovered" this enzyme when trying to cope with an abundance of hydrogen peroxide in the environment.
Some geochemists believe that hydrogen peroxide was abundant at this time as a result of intensive solar radiation on glaciers that covered much of Earth.
"In the glacial melt waters you would have a high concentration of hydrogen peroxide and that would be gradually exposing a number of the primitive organisms (alive at that time)," Caetano-Anolles explained.
The appearance of manganese catalase, an enzyme that degrades hydrogen peroxide and generates oxygen as a byproduct, makes it a likely "molecular culprit for the rise of oxygen on the planet," he added.
The finding was reported in the journal Structure. (ANI)
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