oliglyceric acid synthesis by auto condensation of glyceroyl thioester

8/2/2019 Oliglyceric Acid Synthesis by Auto Condensation of Glyceroyl Thioester

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Summary: The autocondensation of the glyceroyl thioester, S-glyceroyl-ethane-thiol, yielded oligoglyceric acid. The rates of autocondensation and hydrolysisof the thioester increased from pH 6.5 to pH 7.5 in 2,6-lutidine and imidazolebuffers. Autocondensation and hydrolysis were much more rapid in imidazolebuffers as compared to 2,6-lutidine and phosphate buffers. The efficiency ofester bond synthesis was about 20% for 40 mM S-glyceroyl-ethanethiol in 2,6-lutidine and imidazole buffers near neutral pH. The size and yield of theoligoglyceric acid products increased when the concentration of the thioesterwas increased. The relationship of these results to prebiotic polymersynthesis is discussed.

Key words: Glyceroyl thioester - Polymerization - Polyester - Oligoglycericacid - Thioester - Prebiotic chemistry - Molecular evolution.

Abbreviations: Glc, glyceric acid (Glc)n, glyceric acid oligomers wheren = chain length; Glc-SEt, S-glyceroyl-ethanethioli (Glc>2-SEt, S-glyceroyl-glyceroyl-ethanethiolj (Glc)3-SEt, S-Glyceroylglyceroylglyceroyl-ethanethioliGlc-Hydrox, glyceric acid hydroxamatei Glc-Im, N-glyceroyl-imidazolei Im,imidazolei DMF, N,N-dimethylformamide.

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IntroductionIn an effort to understand how energy was produced for the origin of life,

we have studied chemical reactions that resemble the initial energy-yieldingreaction of the glycolysis. Since this glycolytic reaction involves the oxida-tion of glyceraldehyde-3-phosphate to give an 'energy-rich' glyceroyl thioesterwhich is used to drive the synthesis of ATP, we have studied the nonenzymaticformation of thioesters from glyceraldehyde and a thiol, and have examinedthioester-driven phosphoanhydride synthesis. We showed that glyceraldehyde anda thiol could be converted to lactoyl thioester under anaerobic conditions andglyceroyl thioester in the presence of oxygen (Weber 1984a, b). We also ob-tained evidence of alanyl thioester synthesis in similar anaerobic reactions inthe presence of ammonium ion (Weber 1985). Our studies of thioester-drivenphosphoanhydride synthesis demonstrated that thioesters can act as an energysource for the synthesis of pyrophosphate, tripolyphosphate, and phosphorylimi-dazole (Weber 1981, 1982).

Glyceraldehyde's role in prebiotic chemistry may not have been limited toits being an energy source for phosphoanhydride synthesis. Our earlier studiesindicate that glyceraldehyde could act as a source of both energy and monomersfor the synthesis of prebiotic macromolecules, since lactoyl, glyceroyl, andalanyl thioesters derived from glyceraldehyde are in fact 'activated' monomerswhich have the energy needed for polymerization to polyesters or polyamides.Amino acid thioesters have previously been shown to condense to give peptides(Weber and Orgel, 1979). We now report the autocondensation of an hydroxy acidthioester, Glc-SEt, that yields oligoglyceric acid.the synthesis of glyceraldehyde on the primitive Earth most likely occur-red by the oligomerization of formaldehyde (Gabel and Ponnamperuma, 1967| Reidand Orgel 1967| Mizuno and Weiss 1974). Formaldehyde has been synthesized

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placed in vials that contained 20 ml of scintillator made with Liquifluor (NewEngland Nuclear), and counted in a Beckman scintillation counter. Radioactiveproducts were identified by co-chromatography with commercially available stan-dards, whenever possible. Organic acids were detected by spraying with methylred. Thioesters were seen as dark spots under ultraviolet light.

Preparation of L-[14clglyceric acid. A modified version of the method ofLok et_al. (1976) was used to synthesize L-[14C]glyceric acid from L-[14C]-serine. L-Serine (10.3 mg, 0.098 mmole) and 12 nl of concn HC1 were added to asolution of L-[14c(U)]serine (25 ^Ci- 1>7 J^1) in *60 ml water. The solu-tion was cooled to 2c and then sodium nitrite (7.0 mg, 0.1 mmole) was added in1.0 mg portions every 30 min. The reaction solution was allowed to stand 24 hin a cold room at 9C. Two more 1.0 mg additions of sodium nitrite were madeand the reaction solution was allowed to stand at 9C for 24 h and at ambienttemperature for an additonal 24 h. Purification of L-[14c]glyceric acid wasachieved by paper chromatography on Whatman 3MM paper [Rf = 0.57; developingsolvent: tert-butyl alcohol-formic acid-water, 7:1.5:1.5, v/v/v]. [l^Clglycericacid was eluted from the paper with water which was removed in vacuo. The resi-due was redissolved in 1.2 ml of water and the solution filtered through aCentrex microfiltration unit (nylon filter, 0.2 jim pore size, Schleicher andSchuell). The water was removed in vacuo and the residue dried in a desiccatorover P205 and NaOH pellets for 24 h. The residue was dissolved in 300 jil DMF.The yield of L-[14c]glyceric acid was 34% based on radioactivity.

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tions. Nature (London) 216:455Rochester CH (1971) Acidity and inter- and intra-molecular H-bonds. In: Fatal S

(ed) The chemistry of the hydroxyl group, pt 1. Interscience Publishers,London, p 327

Sridharan R, Mathai IM (1974) Transesterification reactions. J Sci Ind Res33:178-187

Stadtman ER (1954) On the energy-rich nature of acetyl imidazole, an enzymatic-ally active compound. In: McElroy WD, Glass B (eds) The mechanism ofenzyme action. John Hopkins Press, Baltimore, p 581

Stadtman ER (1957) Preparation and assay of acyl coenzyme A and other thiolestersi use of hydroxylamine. In: Colowick SP, Kaplan NO (eds) Methods inenzymology, vol III. Academic Press, New York, p 931

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Thompson AR (1951) Separation of saturated mono-hydroxamic acids by partitionchromatography on paper. Aust J Sci Res, Ser B 4:181-1186

Weber AL (1981) Formation of pyrophosphate, tripolyphosphate, and phosphoryl-imldazole with the thioester, N,S-diacetylcysteamine, as the condensingagent. J Mol Evol 18:24-29

Weber AL (1982) Formation of pyrophosphate on hydroxyapatite with thioesters ascndensing agents. BioSystems 15:183-189

Weber AL (1984a) Nonenzymatic formation of 'energy-rich' lactoyl and glyceroylthioesters from glyceraldehyde and a thiol. J Mol Evol 20:157-166

Weber AL (1984b) Prebiotic formation of 'energy-rich' thioesters from glycer-aldehyde and N-acetylcysteine. Origins Life 15:17-27

Weber AL (1985) Alanine synthesis from glyceraldehyde and ammonium ion inaqueous solution. J Mol Evol 21:351-355

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Table 1: Chromatographic and electrophoretic mobilities3

Relative MobilitySubstanceGlc(Glc)2(Glc)3(Glc)4(Glc)5(Glc)>5Glc-SEt(Glc)2-SEt(Glc)3-SEtGlc-Hydrox

System 11.000.740.500.320.21

0-0.212.121.931.570.55

System 21.000.840.650.470.33

0-0.33---^

System 31.000.770.620.520.46

0-0.40---~

Mobilities are given relative to glyceric acid.

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Table 4. Effect of metal ions on the autocondensation of 40 mM Glc-SEt at pH7.0 and ambient temperature.

Percentage of total cpmBuffer Salt

0.4 M Imidazole NaClMgCl2CaCl2ZnCl2

0.4 M 2,6-Lutidine NaClMgCl2CaCl2ZnCl2

Time(days)05100510051005100510051005100510

Glc-SEt

97.97.40.898.27.50.598.37.10.497.912.61.798.382.668.598.282.367.998.482.166.798.267.142.5

Glc0.569.281.30.470.984.40.672.285.90.668.182.70.711.120.30.711.922.20.711.822.80.824.645.7

(Glc)20.819.616.40.618.414.00.418.012.60.716.514.50.55.19.30.54.78.40.54.89.10.67.410.8

(Glc)30.83.61.50.93.21.20.72.81.10.82.71.20.61.21.70.51.21.50.41.21.40.51.11.1

oliglyceric acid synthesis by auto condensation of glyceroyl thioester

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