In the first billion years, there was no oxygen on Earth. Life developed in an anoxic environment. There also seems to have been a kind of "oxygen-free respiration."
This was suggested by studies on primordial microbes that are still found in anoxic habitats today.The enzyme responsible for this type of respiration was unknown until a research team from Goethe University in Germany, has determined and isolated it in a bacterium called Thermotoga maritime. This is perhaps the oldest enzyme in cellular respiration.
The study was published in the latest issue of the Communications Biology journal.
"We already saw ten years ago that there are genes in these microbes called "Rnf" that perhaps encode for a primordial respiration enzyme. Since then, we – as well as other groups worldwide – have attempted to prove the existence of this respiratory enzyme and to isolate it," explains Professor Volker Müller from the Department of Molecular Microbiology and Bioenergetics at Goethe University, in a report published on the university's website.
For a long time unsuccessfully because the complex was too fragile and fell apart at each attempt to isolate it from the membrane. But through hard work and perseverance, researchers Martin Kuhns and Dragan Trifunovic then achieved a breakthrough in two successive doctoral theses.
"In our desperation, we said we should try again. At some point, we took a heat-loving bacterium, Thermotoga maritima, which grows at temperatures between 60 and 90°C. Thermotoga also contains Rnf genes, and we hoped that the Rnf enzyme in this bacterium would be a bit more stable. Over the years, we then managed to develop a method for isolating the entire Rnf enzyme from the membrane of these bacteria," explains Trifunovic.
As the researchers report in their current paper, the enzyme complex functions a bit like a pumped-storage power plant that pumps water into a lake higher up and produces electricity via a turbine from the water flowing back down again.
Only in the bacterial cell, the Rnf enzyme transports sodium ions out of the cell's interior via the cell membrane to the outside and in so doing produces an electric field. This electric field is used to drive a cellular "turbine" that allows the sodium ions to flow back along the electric field into the cell's interior and in so doing it obtains energy.
"Our studies thus radiate far beyond the organism Thermotoga maritime. We're meanwhile able to produce the Rnf enzyme ourselves using genetic engineering methods," explains Müller.