| The synthesis of oligomeric biomolecules such as peptides is the key step marking the evolution from prebiotic chemistry to biochemistry (Imai et al., 1999, Amend and Helgeson, 2000). While monomer synthesis has been demonstrated to proceed in high-energy impact shock, lightning, cavitation or UV-radiation dominated environments (Chyba and Sagan, 1993; Oberbeck et al., 1991; Anbar, 1968), monomer oligomerization requires lower energy yields (Kawamura, 2001; Yokoyama et al., 2003), typically found in geological settings such as deep-sea hydrothermal environments (DSHE). On the basis of these findings and the identification of hyperthermophilic bacterial lineages at the deepest branches of the phylogenetic tree (Di Giulio, 2001), hydrothermally-driven peptide synthesis has been proposed (Huber and Wächtershäuser, 1999, Huber et al., 2003) so as to reduce the nominal 18 ± 3kJ·mol−1 required for the formation of a single peptide bond in diglycine at 25°C (Liebman et al. 2000). In particular, increasing temperatures are predicted to shift the thermodynamic equilibrium between amino acids and product peptide as well as between precursor and successor peptide toward the product oligopeptide (Shock, 1990; 1992; Amend and Helgeson, 2001), however, this hypothesis has not been tested experimentally. Here we demonstrate the formation of short peptides from the amino acid glycine in the temperature range 160°C to 260°C and 200 bar, conditions typical of DSHE. We show that glycine and product peptides enter into equilibrium and demonstrate a lowering of the Gibbs energies for the formation of diglycine and the lactame diketopiperazine from glycine, respectively. Our results confirm that the thermodynamic stability of peptide bonds increases under hydrothermal conditions (Shock, 1992). They support a high temperature origin of life and the early emergence of peptides during chemical evolution. |
