Abstract EANA2024-33

There is currently a great deal of life on Earth. However, the origin of life on Earth is still unknown. Since 1969, more than 100 amino acids and hydrocarbons have been detected in the meteorite that fell on Murchison, Australia. It is clear that amino acids, which are the minimum unit necessary to maintain living organisms, exist in the universe, but only dimers of glycine have been reported for the existence of peptides. I thought that if peptide formation could be demonstrated in the space environment, it would provide a clue to the study of the origin of life. As a first step, we decided to perform space exposure of amino acids on the International Space Station (ISS).

L-Alanine and a mixture of L-alanine and D,L-serine were used the amino acids used in the experiments. Amino acid thin films were formed on MgF2 substrates by vapor deposition. In the ground experiments, the amino acid thin films were exposed to 172 nm VUV radiation by a Xe excimer lamp under vacuum conditions. The MgF2 substrates were installed in the TANPOPO exposure units and exposed on the ISS for several months. The degradation of amino acids during the reaction was monitored by FT-IR. The formation of dipeptides was confirmed by LC-MS analysis of the solution extracted with water from the substrate after the reaction.

First, UV irradiation of alanine thin films confirmed the formation of alanine dimers, as previously reported. All possible dipeptides, alanine dimer, serine dimer, and alanine-serine dimer were detected in the extract of the irradiated sample of alanine and serine mixtures. In addition, all trimeric peptides were detected except the trimer of serine. The amount of alanine dimers increased up to 2 hours of irradiation. However, the amounts of other peptides, were synthesized at a maximum of 30 minutes and decreased after 1 hour of irradiation. This may be due to the fact that the synthesis and degradation occur simultaneously by the VUV irradiation, and the rates of synthesis and degradation were different for dipeptide species. Four peaks of the alanine-serine dimer were detected. This is due to the synthesis of diastereomers by the racemization of amino acids caused by VUV irradiation. Furthermore, alanylalanine was detected in the space exposure of alanine thin film in Tanpopo.

Amino acid monomers were used in those experiments, and dimers of amino acids would be also studied to further elongation and degradation of dimers. In addition, diastereomeric analysis would proceed.