Alanine enantiomers in the Murchison meteorite

Engel and Macko1 have reported that alanine indigenous to the Murchison meteorite has an l-enantiomer excess of about 33%. Furthermore, they reported very similar δ15nitrogen values for l-alanine and d-alanine; these values are quite high in comparison with those of terrestrial amino acids. On this basis, they argued that contamination of the meteorite by terrestrial l-alanine can be ruled out because, if it contributed to the l-enantiomer excess, the lower 15N content of terrestrial l-alanine would significantly lower the δ15N value that they observed for l-alanine.