THE STEREOCHEMISTRY OF AMINO ACIDS IN THE MURCHISON METEORITE

Abstract

The questions of how, where and when life originated in our solar system remain largely unanswered. Some advances have been made with respect to abiotic synthesis of the key molecules deemed essential for the construction of a living cell. In particular, a variety of plausible mechanisms have been suggested for the synthesis of amino acids, the building blocks of peptides and proteins. Laboratory simulation experiments result in the synthesis of racemic amino acids. However, life as we know it is based almost exclusively on l-enantiomers rather than racemic mixtures of d- and l-enantiomers. A partial solution to this problem may be that the l-enantiomer excess essential for life's origin on Earth was introduced from elsewhere in the solar system. For the past 20 years we have investigated the stereochemistry of amino acids in stones of the Murchison meteorite. Many of the common protein amino acids in Murchison are not racemic (l-enantiomer excess) and, based on their overall distribution and respective stable isotope compositions, do not appear to be artifacts of terrestrial contaminants (i.e. l-amino acids) introduced subsequent to impact. We hypothesize that comet and meteorite impacts during the early stages of Earth's formation provided at least some of the essential components with the correct stereochemistry for the origin of life.