Salt-induced peptide formation reaction has been suggested
to be prebiotically relevant BAY 63-2521 clinical trial for the very first steps of chemical evolution (Schwendinger and Rode 1989). Based on Monte Carlo computer simulations, Rode and co-workers found that sodium chloride at concentrations above 3 M effectively acts as a dehydrating agent to overcome the thermodynamic barrier of peptide bond formation in aqueous solutions, and the first this website hydration shell of the sodium ion was assumed to no longer be saturated with water molecules (Jakschitz and Rode 2012). Furthermore, using HPLC-MS/MS analysis, a high concentration of sodium chloride was found to significantly enhance the formation of peptides from L-glutamic acid (L-Glu) in homogenous water solutions (Wang et al. 2005). All the references we have found that discuss the presence of other mono- and divalent inorganic cations in prebiotic peptide formation speculate that these
ions support the dehydrating effect of sodium chloride. However, the level of potassium exceeds that of sodium by more than an order of magnitude inside all living cells (Aronson et al. selleck inhibitor 2009), and the ion ratio is actively preserved with Na+/K+ pumps in the cell membrane, which suggests that potassium is more essential for life. The physical-chemical differences between Na+ and K+ are small (Freedman 1995), although the bio-directed activity of these ions differs dramatically; for example, K+ is required for ribosomal peptide synthesis (Spirin and Gavrilova selleck screening library 1971) and the amplification of DNA with thermostable Taq polymerase (Saiki et al. 1988), whereas Na+ attenuates these processes. The contradiction between the Na+ and K+ compositions of seawater and living cell cytoplasm led
to the hypothesis that the first protocell could have emerged in KCl solution (Natochin 2007; Natochin 2010). However, the hypothesis of the K+-driven emergence of prebiotic peptides remains to be tested. Here we investigate the relative effects of Na+ and K+ in a model peptide synthesis reaction. Methods L-glutamic acid and 1,1′-carbonyldiimidazole (CDI) were obtained from Sigma-Aldrich Co. LLC (St. Louis, USA). In total, 10 mmol KCl or 10 mmol NaCl was added to reaction mixtures containing 3 mmol L-Glu in 5 ml distilled water. The mixture was diluted to 10 ml and cooled on a crashed ice-NaCl mixture, and 6 mmol CDI was added into each mixture and incubated at room temperature for 24 h. A 10 μl sample was loaded onto a Zorbax SAX (4.6 mm × 250 mm, 5 μm) column using an autosampler. Peptide separation was performed at a flow rate of 0.5 ml/min using an NaCl gradient (2–80 % B for 80 min; buffer A: 20 % acetonitrile in 0.020 M NaH2PO4 at pH 7.0; buffer B: 2.0 M NaCl in buffer A) using an Agilent 1100 nano-HPLC system (Agilent Technologies Inc., USA). LC analysis of the peptides was performed by an established procedure (Ishihama et al.