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Using photochemical processing
techniques, teams of Dutch, French (CNRS), and German*
researchers have succeeded in synthesizing 16 amino acids in conditions
that mimic those found in the interstellar medium. The role of extraterrestrial
compounds in the appearance of life on Earth is currently the focus of
much debate. These teams' findings support the suggestion that prebiotic
molecules (molecules predating the appearance of life on Earth) could
have been deposited on the Earth’s surface by meteorites, comets,
or other interstellar particles. This research is published in the March
28th issue of Nature.
Amino acids are the building
blocks of proteins and probably played a key role in the appearance of
life on Earth. All the proteins of living organisms are composed of 20
basic amino acids. It is thought that certain amino acids were already
present when life appeared some four billion years ago. At that time,
they could have been formed in the Earth’s atmosphere and/or in the
ocean’s hydrothermal systems. As some of these amino acids were found
in carbonaceous meteorites, the contribution of extraterrestrial amino
acids synthesized in interstellar space and delivered to Earth in the
form of cometary dust offers an attractive alternative to a purely terrestrial
origin of life on Earth.
To support this hypothesis, a mixture containing ice crystals of water,
ammonia, methanol, carbon monoxide and dioxide was irradiated at the Leiden
Laboratory for Astrophysics in Holland, in conditions that mirrored those
found in interstellar space (high vacuum chamber at - 261°C). After
warming the samples to room temperature, the residue was analyzed at the
CNRS "Centre de Biophysique Moléculaire" in Orleans with
gas chromatography-mass spectrometry (GC-MS). The scientists identified
16 amino acids, six of which are among the 20 protein-constituent amino
acids (glycine, alanine, valine, proline, serine, and aspartic acid).
The amino acids produced by photosynthesis showed enantiomeric separation
(as many “left-handed” forms as “right-handed”), contrary
to that found in all proteins of living organisms in which only one of
these forms is present, the “left-handed” form. This would exclude
contamination from biological amino acids, which are all “left-handed”.
Special precaution was taken to eliminate risk of biological contamination:
carbon monoxide and dioxide were replaced by their carbon 13 counterparts,
which involved increasing the mass of each carbon atom by one unit. This
gave the resulting amino acids a different signature, distinguishing them
from biological amino acids of terrestrial origin. The compounds corresponding
to these mass increases were indeed identified.
The publication in Nature of these results is a manifestation of
the fruitful cooperation between the Leiden Laboratory for Astrophysics,
which studies interstellar medium chemistry, and the Exobiology team of
the "Centre de Biophysique Moléculaire," which is involved
in origin-of-life chemical studies. Two German teams from Ketlenburg-Lindau
and Bremen, specialized in the analysis of cometary components, also participated
in the design of these studies.
*
- Raymond and Beverly Sackler Laboratory for Astrophysics at Leiden Observatory,
Leiden – The Netherlands
- Centre de biophysique moléculaire, CNRS – Orléans,
France
- Max-Planck-Institut für Aeronomie, Katlenburg-Lindau – Germany
- Bremen University, Department of Physical Chemistry, Brême –
Germany
References: G.M. Muñoz Caro, U.J Meierhenrich, W.A Schutte,
B. Barbier, A. Arcones Segovia, H. Rosenbauer,
W.H -P. Thiemann, A. Brack, J.M Greenberg. Amino acids from ultraviolet
irradiation of interstellar ice analogues. Nature, vol. 416, pp.
403-406, 28 March 2002.
Researcher
Contacts:
"Centre de biophysique moléculaire"
CNRS - Orleans
Bernard Barbier – Tel: +33 2 38 25 55 77
André Brack – Tel: +33 2 38 25 55 76
Chemical Sciences Department Contact:
Laurence Mordenti
Tel: +33 1 44 96 41 09
Press contact :
Martine Hasler
Tel : +33 1 44 96 46 35
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