The origin of life is seen as the formation of the first biomolecules capable of multiplication and further development. Until now it was unclear which reactions may have triggered the evolution of this primitive metabolism. Scientists at the Technische Universitaet Muenchen (TUM) have now revealed mechanisms by which a few biomolecules may bring forth new products in a kind of avalanche to initiate a self-expanding metabolism.
Volcanic-hydrothermal flow channels provide chemically unique environments that, at first sight, appear hostile to life. They are defined by cracks in the crust of Earth through which water flows, laden with volcanic gases in contact with diversity of minerals. And yet -- it is precisely this extreme environment in which the two mechanisms at the root of all life may have emerged: The multiplication of biomolecules (reproduction) and the emergence of new biomolecules on the basis of previously formed biomolecules (evolution).
The first link of the chain of reactions that led eventually to the formation of cellular forms of life comprises only a few amino acids formed from volcanic gases through mineral catalysis. Akin to a domino stone that triggers an avalanche, these first biomolecules stimulate not only their own further synthesis but also the production of entirely new biomolecules. "In this manner life begins by necessity in accordance with the pre-established laws of chemistry and in a pre-determined direction," declares Günter Wächtershäuser, honorary professor for evolutionary biochemistry at the University of Regensburg. He developed the mechanism of a self-generating metabolism -- theoretically. Alas, an experimental demonstration had been lacking so far.
Now, a team of scientists working with Claudia Huber and Wolfgang Eisenreich, at the Chair of Biochemistry in the Department of Chemistry at the Technische Universitaet Muenchen, in close cooperation with Wächtershäuser, has managed for the first time to demonstrate experimentally the possibility of such a self-stimulating mechanism. A catalyst comprising compounds of the transition metals nickel, cobalt or iron plays the lead role in these reactions. It provides not only for the formation of the first biomolecules, but it also initiates the chain of reactions. The reason: The biomolecules newly formed from the volcanic gases engage the center of the transition metal catalyst to enable further chemical reactions that bring forth entirely new biomolecules. "This coupling between the catalyst and an organic reaction product is the first step," explains Wächtershäuser. "Life arises when, subsequently, a whole cascade of further couplings takes place. And this primordial life leads eventually to the formation of genetic material and to the first cells."
The scientists simulated in their experiments the conditions of volcanic-hydrothermal flow channels and established an aqueous organometallic system that produces a whole range of different biomolecules, among them the amino acids glycin and alanin. Here the carbon source was provided by a cyano compound and the reducing agent by carbon monoxide. Nickel compounds turned out to be the most effective catalysts in these experiments. The scientists then added the products glycin and alanin to another system, which, in turn, generated two new biomolecules. The result: The two amino acids increased the productivity of the second system by a factor of five.
In future experiments the scientists intend to recreate more precisely the conditions of volcanic-hydrothermal systems that life could have arisen in billions of years ago. "To this purpose we first simulate certain stages in the development of a volcanic-hydrothermal flow system in order to determine essential parameters," explains Wächtershäuser. "Only thereafter we may engage in a rational construction of a flow reactor."
The results of the team of scientists headed by Wächtershäuser and Eisenreich show that the origin and evolution of life in hot water of volcanic flow ducts is feasible. The results reveal advantages of the theory in contrast to other approaches. In the flow ducts temperature, pressure and pH change along the flow path, and thereby a graded spectrum of conditions is created that is appropriate for all stages of early evolution up to the formation of genetic material (RNA/DNA).
The most important property of the system is its autonomy: As opposed to the notion of a cool prebiotic broth, the first metabolism was not dependent on accidental events or an accumulation of essential components over thousands of years. Once the first domino stone is toppled, the others follow automatically. The origin of life proceeds along definite trajectories, pre-established by the rules of chemistry -- a chemically determined process that gives rise to the tree of all forms of life.
This work was funded by the Deutsche Forschungsgemeinschaft (WA- 983/3, WA-983/4 and EI-384/3-1), the Hans-Fischer Gesellschaft and the Fonds der Chemischen Industrie.
- Claudia Huber, Florian Kraus, Marianne Hanzlik, Wolfgang Eisenreich, Günter Wächtershäuser. Elements of Metabolic Evolution. Chemistry - A European Journal, 2012; DOI: 10.1002/chem.201102914
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