Dr. Claudia Huber with one of the autoclaves, in which the reactions were carried out. |
The
origin of life is seen as the formation of the first biomolecules which
may be subject to multiplication and further development. Hitherto it
was unclear, which reactions could have triggered the evolution of this
ur-metabolism. Now scientists at Munich Technical University (TUM)
revealed mechanisms by which a few biomolecules may bring forth new
products in the style of an avalanche to initiate a self-expanding
metabolism. Chemistry—A European Journal has published their results.
Volcanic-hydrothermal
flow channels offer a chemically unique environment, which at first
glance appears hostile to life. It is defined by cracks in the crust of
the earth, through which water flows, laden with volcanic gases are
contacting a diversity of minerals. And yet—it is precisely this extreme
environment, where the two mechanisms could have emerged, which are at
the root of all life: The multiplication of biomolecules (reproduction)
and the emergence of new biomolecules on the basis of previously formed
biomolecules (evolution).
At
the outset of this concatenation of reactions that led eventually to
the formation of cellular forms of life there are only a few amino
acids, which are formed from volcanic gases by mineral catalysis. Akin
to a domino stone that triggers a whole avalanche, these first
biomolecules stimulate not only their own further synthesis but also the
production of wholly new biomolecules.
“In
this manner life begins by necessity in accordance with pre-established
laws of chemistry and in a pre-determined direction,” says Günter
Wächtershäuser, honorary professor for evolutionary biochemistry at the
University of Regensburg. He developed the theoretical mechanism of a
self-generating metabolism. Until now, an experimental demonstration has
been lacking.
Scientists
around Claudia Huber and Wolfgang Eisenreich, chair of biochemistry in
the Department of Chemistry at the TUM and in close cooperation with
Wächtershäuser, have managed for the first time to demonstrate
experimentally the possibility of such a self-stimulating mechanism. A
catalyst consisting of compounds of the transition metals nickel, cobalt
or iron has the lead role in these reactions. It provides not only for
the formation of the first biomolecules, but it also initiates the
concatenation of reactions. The reason: The biomolecules just newly
formed from the volcanic gases engage the center of the transition metal
catalyst to enable further chemical reactions bringing forth wholly new
biomolecules.
“This
coupling between the catalyst and an organic reaction product is the
first step,” explains Wächtershäuser. “Life arises, if subsequently a
whole cascade of further couplings takes place, and this primordial life
leads eventually to the formation of genetic material and of 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 suite 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, that generated again two new
biomolecules. The result: The two amino acids increased the productivity
oft he second system by a factor of five.
In
future experiments the scientists intend to recreate more precisely the
conditions of volcanic-hydrothermal systems, wherein life could have
arisen billions of years ago. “For this purpose we simulate first
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 scientists around Wächtershäuser and Eisenreich show
that an origin and evolution of life in hot water of volcanic flow ducts
is feasible. The results reveal advantages of the theory compared to
other approaches. Within the flow ducts temperature, pressure and pH
change along the flow path, and thereby a graded spectrum of conditions
is offered 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 both, the first metabolism was not
dependent on accidental events or an accumulation of essential
components over thousands of years. As soon as the first domino stone is
toppled, the others will follow automatically. The origin of life
proceeds along definite trajectories, pre-established by the rules of
chemistry—a chemically determined process giving rise to the tree of all
forms of life.
