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Ehrenfreund, P, Glavin DP, Botta O, Cooper G, Bada JL.  2001.  Extraterrestrial amino acids in Orgueil and Ivuna: Tracing the parent body of Cl type carbonaceous chondrites. Proceedings of the National Academy of Sciences of the United States of America. 98:2138-2141.   10.1073/pnas.051502898   AbstractWebsite

Amino acid analyses using HPLC of pristine interior pieces of the Cl carbonaceous chondrites Orgueil and Ivuna have found that beta -alanine, glycine, and gamma -amino-n-butyric acid (ABA) are the most abundant amino acids in these two meteorites, with concentrations ranging from approximate to 600 to 2,000 parts per billion (ppb). Other alpha -amino acids such as alanine, alpha -ABA, alpha -aminoisobutyric acid (AIB), and isovaline are present only in trace amounts (<200 ppb). Carbon isotopic measurements of -alanine and glycine and the presence of racemic (D/L approximate to 1) alanine and beta -ABA in Orgueil suggest that these amino acids are extraterrestrial in origin. In comparison to the CM carbonaceous chondrites Murchison and Murray, the amino acid composition of the Cls is strikingly distinct, suggesting that these meteorites came from a different type of parent body, possibly an extinct comet, than did the CM carbonaceous chondrites.

Elsila, JE, Glavin DP, Dworkin JP, Martins Z, Bada JL.  2012.  Inconclusive evidence for nonterrestrial isoleucine enantiomeric excesses in primitive meteorites. Proceedings of the National Academy of Sciences of the United States of America. 109:E3288-E3288.   10.1073/pnas.1213261109   Abstract

Pizzarello et al. (1) recently described the soluble organic content of eight Antarctic Renazzo-type (CR) carbonaceous chondrites and reported large enantiomeric excesses (ee) of l-isoleucine and d-alloisoleucine. The reported values of ee decrease with inferred increases in aqueous alteration. We believe the conclusions presented in the paper are not fully justified and the data are potentially flawed.

Potential terrestrial contamination of meteoritic amino acid data must always be considered. The manuscript states that “terrestrial contamination levels… were evaluated based on the presence of proteinogenic amino acids’ l-excesses and accounted for when needed,” but this “accounting” is not described. A wide range of l-proteinogenic amino acid excesses was measured …