Demonstrating Prebiotic Peptide Evolution by Nitrogen Isotope Discrimination in an Autocatalytic Chemical Reaction Network

Nitrogen isotope discrimination may be closely related to the prebiotic evolution of peptides that occurred in the origin of life from chemical reaction networks (CRNs). We deduce that autocatalytic Sammox (sulfurous reduction coupled to anaerobic ammonium oxidation)-driven CRN is a feasible scenario for life origin. To demonstrate prebiotic peptide evolution, we investigated N isotope discrimination in proteinogenic amino acids and peptide synthesis in Sammox-driven CRNs, combining mathematical and physical models. The species and amounts of proteinogenic amino acids generated in Sammox-driven CRNs with 14NH4+ as the N source were all significantly higher than those in Sammox-driven CRNs with 15NH4+ as the N source for both hydrothermal and microaerobic eutectic freezing conditions. The low yield of 15N-amino acids, both species and amounts, will lead to the formation of 15N-peptides with poor structure and function and slow peptide dynamics; these peptides might be preferentially degraded in Sammox-driven CRNs. We then explored the nitrogen isotopic effects during the synthesis process from ammonia to glycine, from glycine to glycine-containing peptides, and during the process of glycine-containing peptide hydrolysis. 15N are eliminated in competition with 14N during the process of glycine synthesis, glycine-containing peptide synthesis, and glycine-containing peptide hydrolysis under hydrothermal conditions as determined by the maximum entropy production principle, which is a prebiotic evolution process. In addition, pyrrole as the building block of the prosthetic group, which is generated from Sammox-driven CRNs under hydrothermal conditions, may provide a more evolutionary possibility of prebiotic peptides.