STUDY SHOWS PRECURSORS COULD HAVE CREATED COMPLEX METABOLISM

New work from researchers at the Earth-Life Science Institute (ELSI) at Tokyo Institute of Technology (TIT), shows that a simple compound that can be found in some modern volcanic gases -- a thioacid (a compound formed from an organic acid and hydrogen sulfide, which is the compound largely responsible for the "rotten egg" smell of many hot springs) -- readily reacts with simple sulfur containing thiol compounds similar to those fundamental to modern metabolism to form reactive thioesters similar to those found in modern biology. 

This reaction happens readily in water and may have served as a starting point for the evolution of more complex biochemistry. During the research, they found that when they included iron (which is the most abundant element on Earth and comprises about 5% of Earth's surface layer, known as the crust), in their reactions, the reaction product yields increased, ScienceDaily reported. The study was also published in the journal Chemical Communications. 

The team suggests this may mean energy coupling between multiple reactions, in which one reaction drives another forward, may have its origins in non-living environmental chemistry. Remarkably, they also found a side product of the reaction they discovered can be used to make a second type of versatile energy-coupling compound required by all living things: FeS (short for iron-sulfur) clusters. These are small aggregates of only a few atoms each of iron and sulfur, which help organisms metabolize as they move electrons from one molecule to another. One important example of such a FeS-cluster-using-pathway is photosynthesis, which transfers electrons from water to CO2 to make sugars and oxygen. This work thus provides a new understanding of how high energy molecules and electron transfer reactions may have been naturally produced as early metabolism was evolving. 

Understanding this energy exchange could be as important as understanding the origin of building blocks, so the ELSI team decided to search for reactions which could be coupled together energetically. As lead author, Sebastian Sanden notes "We were already studying FeS minerals, and we knew how easy their formation was, so we wanted to see if we could couple this excess wasted energy to another reaction." The thioacid they began their study with contains sulfur, which they knew then only had to be reacted with iron to make the FeS clusters they were already studying. While this work may shine new light on how naturally occurring energy exchange reactions may have helped "jump-start" metabolism, it may also be important for the field of "green chemistry," which is concerned with finding the most energetically effective and environmentally friendly methods to make chemical compounds. While toxic heavy metals like cadmium and mercury and solvents like chloroform are often used in industrial organic chemistry, the reactions discovered by this research group are very efficient and work in water using non-toxic iron as a catalyst.