Distribution and enantiomeric composition of amino acids in the Murchison meteorite

Abstract

Early determinations of the amino acid distribution in water extracts of the Murchison meteorite revealed unusual amino acids, including isovaline (Ival), α-aminoisobutyric acid (α-Aiba) and pseudoleucine (Ple), as well as common ones such as glycine (Gly), alanine (Ala) and glutamic acid (Glu)1–10. Amino acids that could be resolved into their respective D- and L-enantiomers were reported to be racemic (see, for example, refs 1, 3, 5), although small sample size might have hindered the precise determination of D/L values. Using improved chromatographic and mass spectrometric procedures we have now been able to amplify and resolve the partially racemized amino acids, Glu, aspartic acid (Asp), proline (Pro), leucine (Leu) and Ala, in an interior sample of a Murchison meteorite stone. Water-extractable amino acids were more racemized than those recovered by digesting the water-extracted meteorite in 6M HC1. The amino acid composition of this stone was similar to previous reports1–8, including the absence of tyrosine (Tyr), methionine (Met), phenylalanine (Phe) and only minor traces of serine (Ser) and threonine (Thr)9. Serine and Thr are usually considered to be terrestrial contaminations. This is the first report of amino acids in a carbonaceous meteorite which, based on currently accepted criteria, appear to be indigenous but for unknown reasons are not racemic. Confirmation of these findings by other investigators suggests that further examination of amino acids in clean carbonaceous meteorites could be beneficial.