Nonprotein Amino Acids from Spark Discharges and Their Comparison with the Murchison Meteorite Amino Acids

Abstract

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...

Prebiotic selection and assembly of proteinogenic amino acids and natural nucleotides from complex mixtures

“…Accordingly, we examined the reaction of 2-aminothiazole (7) with aldehydes and ketones 2d-w, which are all prebiotic amino acid precursors. 2,[8][9][10][11][12][13] All of the aldehydes furnished their aminals (8d-w) in excellent yield (Table 1). In stark contrast, no ketone aminals precipitated, even after extended incubation.…”

“…[8][9][10][11][12][13] Thus, to investigate 2-aminothiazole (7) induced selective amino acid synthesis, a mixture of eight prebiotic aldehydes and ketones 2 (Fig. 5) was incubated with 2-aminothiazole (7; 10 equiv.…”

“…However, no reported prebiotic synthesis or meteoritic amino acid sample provides the restricted set of amino acids assigned to the genetic code. 2,[8][9][10][11][12][13] For example, Sutherland and co-workers recently demonstrated the stepwise prebiotic syntheses of 12 aminonitrile (13) proteinogenic amino acid precursors, but paradoxically, essential ketones-such as acetone (2o), monohydroxyacetone (2p) and dihydroxyacetone (2q)-are required during assembly of the branched carbon framework of valine and leucine. 13 Ideally ketones would be excluded from prebiotic aminonitrile 13 synthesis because prebiotic ketones undergo aminonitrile formation just as effectively as aldehydes, but α,α-disubstituted amino acids are not genetically encoded (Table 1).…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13] Proteins are built from a highly restricted set of about 20 amino acids according to a universal triplet code of four ribonucleotides. Therefore, it is essential to learn how this specific small constellation of molecules became irrevocably linked at the advent of life.…”

Hydrolysis of Dihydrouridine and Related Compounds

“…DHUR has been found in the urine of rats and is excreted quantitatively (Toppet aL, 1993 The half-life of ring opening of 9 h at 100°C is not that rapid compared to the optimum doubling time of hyperthermophiles, which is i-3 h (Pley et al, 1991;Kurr et al, 1991;Vrlkl et al, 1993 (Wolman et al, 1972) and are also found in the Murchison meteorite (Kvenvolden et ai., 1971;Peltzer et aLo 1984). Small amounts of hydantoic acids and hydantoins have also been found in the Murchison meteorite (Cooper & Cronin, 1995).…”