Twelve nonprotein amino acids appear to be present in the Murchison meteorite. The identity of eight of them has been conclusively established as Nmethylglycine, fl-alanine, 2-methylalanine, a-amino-nbutyric acid, fl-amino-n-butyric acid, 7y-amino-n-butyric acid, isovaline, and pipecolic acid. Tentative evidence is presented for the presence of N-methylalanine, N-ethylglycine, f-aminoisobutyric acid, and norvaline. These amino acids appear to be extraterrestrial in origin and may provide new evidence for the hypothesis of chemical evolution.The formation of organic compounds and their accumulation have been considered to be a necessary preamble to the appearance of life on the primordial earth (1). Various forces, such as ultraviolet light from the sun, heat from volcanos, electrical discharges in the form of lightning, and ionizing radiation from radionuclides acting upon the reducing atmosphere of the primitive earth may have produced a large number of organic compounds until the early oceans had the consistency of a "hot dilute soup" (2-5). Considerations of stellar and planetary evolution lead us to believe that the sequence of events that led to life on earth may have been duplicated elsewhere in innumerable planetary systems in the universe (6-9).In attempting to substantiate this hypothesis, two avenues have generally been used. In the synthetic approach, the conditions of a primitive planet have been simulated in the laboratory. Many of the constituents of proteins and nucleic acids have been synthesized in this manner (10,11 (19,20). The finding of amino acids indigenous to such samples would constitute convincing evidence for extraterrestrial chemical evolution. In our analysis of the Murchison meteorite we have already reported (21) the presence of five amino acids commonly found in protein: glycine, alanine, valine, proline, and glutamic acid, and two not generally found in proteins: N-methylglycine (sarcosine) and aaminoisobutyric acid (2-methylalanine). We have now identified aspartic acid and six additional nonprotein amino acids:13-alanine, a-amino-n-butyric acid, j3-amino-n-butyric acid, -y-amino-n-butyric acid, isovaline, and pipecolic acid. Furthermore, there appears to be tentative evidence for at least four other nonprotein amino acids: j3-aminoisobutyric acid, norvaline, N-methylalanine, and N-ethylglycine.
ANALYSISThe amino acids were obtained from the meteorite by extraction of a pulverized sample with boiling distilled water, followed by acid hydrolysis of the aqueous extract (22). After the removal of inorganic salts from the acid hydrolysate, the resulting material was analyzed for amino acids by ion-exchange chromatography, gas chromatography, and gas chromatography combined with mass spectrometry. The residue left after the water extraction of the meteorite was hydrolyzed with acid and similarly analyzed. In a procedural blank, no amino acids could be detected.A piece of the Murchison meteorite (23) that appeared to be massive in character, and showed signs of the least exter...
