Experts Gain New Insight into How Aerobic Respiration Developed

For a very long time after the first lifeforms developed on Earth, the atmosphere was significantly different from the way it is today. Researchers have been trying to determine how things evolved over time, and a new study now helps shed some more light on the issue.

Japanese investigators at the RIKEN Spring-8 Center in Harima say that they were recently able to decipher the crystal structure of quinol-dependent nitric oxide reductase (qNOR). This bacterial enzyme is responsible for helping microorganisms use nitrate or sulfur as main energy sources.

In our own bodies, aerobic respiration leads to the conversion of oxygen we extract from the air into adenosine triphosphate (ATP), the main energy molecule of the body. But bacteria living in areas of the world without access to oxygen had to adapt to their environments.

The bottom of the ocean is notoriously deprived of oxygen, yet very rich in sulfur and nitrate. This is why lifeforms living there needed to evolve in order to use whatever materials they had access to. The molecule qNOR allows them to do that, by breaking down the two abundant chemicals into ATP.

By deciphering the enzyme's structure, the Japanese researchers have just made a step further in deciphering the mystery of how our earliest oxygen-breathing ancestors evolved. But the study has other applications as well.

For example, one of the main nitrogen oxide sources is the global ocean, and now scientists believe they may use the new data to quantify N2O production more efficiently. The thing about this gas is that it's hundreds of times more potent for underlying global warming than carbon dioxide (CO2).

The reason why the NOR class of proteins was so important for this study is that it accounts for more than 70 percent of the globe's entire N2O production. Over the past few years, more and more investigators have begun turning their attention towards these enzymes.

Another reason that makes studying NOR so important is the fact that these molecules are very similar to cytochrome oxidase (COX), an enzyme heavily involved with a process that is critically-important to aerobic respiration. NOR and COX play similar roles, and may share a common origin.

What the RIKEN team found was that NOR contain what appears to be the ancestors of proton pumps. The latter are electrochemical concentration gradients across cellular membranes, which are used to pump electrons through.

The new discovery implies that anaerobic organisms may indeed have proton pumps, or at least some form of such structures. This indicates that the evolutionary histories linking anaerobic and aerobic organisms are not so different after all, Daily Galaxy reports.