Open Access

Experimental verification of photostability for free- and bound-amino acids exposed to γ-rays and UV irradiation

  • Yoshinori Takano17Email author,
  • Takeo Kaneko27,
  • Kensei Kobayashi27,
  • Daisuke Hiroishi37,
  • Hidematsu Ikeda37 and
  • Katsumi Marumo17
Earth, Planets and Space201456:BF03352529

Received: 14 December 2003

Accepted: 13 June 2004

Published: 24 June 2014


The photo-stability of simulated free and bound amino acids exposed to photon sources of 1.2–1.3 MeV γ-rays from a 60C° source and ultra-violet (UV) irradiation from a 10 eV deuterium lamp was examined. The free amino acids in aqueous solution were drastically decreased while the bound amino acids in aqueous solution were slightly decreased with the duration of γ-rays and UV irradiation. The apparent half-lives (t1/2) of bound serine and threonine under γ-rays irradiation were more than 10.6 and 27.9 times as stable as the free amino acids, respectively. The photo-stability of bound amino acids was greater than that of free amino acids under irradiation by high-energy photons. These results strongly suggest that bound, but not free, amino acids could be found in extraterrestrial environments. Radio- or photo-alteration processes are mainly decomposition pathways, with the production of secondary amino acids via decomposition of the α-carboxylic group; β-alanine and γ-aminobutyric acids, α-decarboxylation products of aspartic acid and glutamic acid, respectively, were detected.

Key words

Photostabilityfree- and bound-amino acidsirradiation experimenthalf-lives