All the nonprotein amino acids found in the Murchison meteorite are products of the action of electric discharge on a mixture of methane, nitrogen, and water with traces of ammonia. These amino acids include a-amino-n-butyric acid, a-aminoisobutyric acid, norvaline, isovaline, pipecolic acid, fl-alanine, 6-amino-n-butyric acid, j#-aminoisobutyric acid, -y-aminobutyric acid, sarcosine, N-ethylglycine, and N-methylalanine. In addition, norleucine, alloisoleucine, N-propylglycine, N-isopropyl-glycine, N-methyl-ft-alanine, N-ethyl-fl-alanine a,j2-diaminopropionic acid, isoserine, a,-y-diaminobutyric acid, and a-hydroxy--y-aminobutyric acid are produced by the electric discharge, but have not been found in the meteorite.A number of amino acids have been found recently in the Murchison meteorite (1-4). The evidence is strong that the meteorite was not contaminated with amino acids after it fell on the earth, since the amino acids are racemic and since many of them do not occur or are rare in terrestrial biology. Several of these meteorite amino acids have been properly demonstrated to be synthesized by the action of electric discharges on CH4, NH3, H20, and H2 (5-7). These include glycine, alanine, sarcosine, f3-alanine, N-methylalanine, a-aminon-butyric acid, and a-aminoisobutyric acid. We have recently repeated the electric discharge experiment (8) and have demonstrated, by modern techniques, the presence of aspartic acid, glutamic acid, valine, isovaline, norvaline, and proline, all of which are found in the meteorite. We have also demonstrated the electric discharge synthesis of leucine, isoleucine, alloisoleucine, norleucine, serine, threonine, allothreonine, a-hydroxy--y-aminobutyric acid, and a,7y-diaminobutyric acid, which have not yet been found in the meteorite, although some of them may be present [e.g., the leucines (3) ].The strong resemblance between the amino acids from the electric discharge and in the meteorite induced us to look for the other nonprotein amino acids found in the meteorite. We have found in the electric discharge reaction all the amino acids so far reported to be present in the meteorite. MATERIALS AND METHODSThe authentic samples of the N-alkylated amino acids were prepared by reaction of the amine with the corresponding haloacid, and recrystallization from alcohol.The same sample of amino acids produced by electric discharge that was used for the identification of hydrophobic amino acids (8) was used in the present analysis. The 18 fractions from the Dowex 50(H+) chromatography were quantitated with an amino-acid analyzer. The amino acids were sufficiently separated to quantitate the ,-alanine, y-aminobutyric acid, isoserine, and a,#%diaminopropionic acid. Sarcosine and N-ethylglycine were quantitated on the aminoacid analyzer with a pH 2.80 buffer; the column eluent and ninhydrin were heated for 30 min instead of the usual 8-min heating period (9). The other amino acids were either present in amounts too small or the color yield was too low to allow quantitation on the amino...
The formation of amino acids by the action of electric discharges on a mixture of methane, nitrogen, and water with traces of ammonia was studied in detail. The presence of glycine, alanine, a-amino-n-butyric acid, a-aminoisobutyric acid, valine, norvaline, isovaline, leucine, isoleucine, alloisoleucine, norleucine, proline, aspartic acid, glutamic acid, serine, threonine, allothreonine, a-hydroxy---aminobutyric acid, and a,-y-diaminobutyric acid was confirmed by ion-exchange chromatography and gas chromatography-mass spectrometry. All of the primary a-amino acids found in the Murchison Meteorite have been synthesized by this electric discharge experiment.Most prebiotic syntheses that start with the primitive atmospheric constituents give substantial yields of glycine, alanine, and a-amino-n-butyric acid (1). Prebiotic syntheses of the higher aliphatic amino acids have been claimed, for example, by the action of electric discharges on CH4 + NH3 + H20 (2-6), by heating CH4 + NH3 + H20 to 900-1200°(7, 8), and by the action of shock waves on CH4, C2H6, NH3, and H20 (9). The amino acids were identified only by an amino-acid analyzer (2-4, 6, 7, 9), only by paper electrophoresis (8), or only by gas chromatography (5). However, these techniques are not sufficient by themselves to identify an amino acid.In the original synthesis of amino acids by electric discharges (10-12), only glycine, alanine, a-amino-t-butyric acid, a-aminoisobutyric acid, and ,B-alanine, of the simple aliphatic amino acids, were synthesized in sufficient yield to obtain identification by a melting point of a derivative. Recently developed techniques permit the identification of compounds found in lower yield by this synthesis.The synthesis under prebiotic conditions of aspartic and glutamic acid (2-8, 12-14), serine (2, 5, 6-8, 13), threonine (2, 3, 5-7), and proline (3, 4, 7, 8, 13) have been reported but they have not been properly identified [except for aspartic acid (14) ]. The synthesis of these amino acids (except proline) has also been reported from the polymerization of HCN (1), but again without proper identification. A prebiotic synthesis of threonine should also yield allothreonine, but this amino acid has never been reported. In addition, several investigators have reported the appearance of a large peak at the isoleucine position on the amino-acid analyzer (2, 4-6, 13). The identification of this peak as isoleucine has been questioned (4, 13). It is evident that this compound cannot be isoleucine, since a corresponding peak for alloisoleucine is not observed.Most electric-discharge experiments have been done with a large amount of ammonia present. Use of nitrogen instead of ammonia in such experiments does not change the major products, although the yield of amino acids is lower (12).The use of a higher concentration of ammonia in such experiments has been criticized (15), and it is now thought that the ammonia concentration in the prebiotic atmosphere was not likely to have been greater than 10-5 atm (16,17). Although this i...
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