THE PERSEUS-EXOBIOLOGY EXPERIMENT ONBOARD MIR

摘要

Two amino acids, L-leucine and "α-methyl-L-leucine; a cyclic dipeptide, L-leucine-diketopiperazine, and an activated tripeptide L-trileucine thioethylester, were exposed for three months to space conditions onboard the MIR station during the Perseus-Exobiology mission in 1999. These samples were exposed in order to study the exogenous hypothesis for the origin of some of the important biological building blocks of life. The four compounds were exposed both free and associated with basalt, clay and meteorite powder to simulate the effects of potential meteorite protection. Post-flight analyses did not reveal any racemization or polymerisation of the exposed compounds. Approximately half of the amino acids were photolyzed with decarboxylation apparently the primary cause. Peptides were less sensitive to photolysis which mainly occurred by decarbonylation, but were partly lost by natural degradation or sublimation. The best mineral protection for the samples was ensured by the meteorite powder, which exhibits the highest absorption in VUV, whereas clay, almost transparent in VUV was the least efficient. By varying the thickness of the meteorite layer, It was determined that a 5 μm film was necessary to ensure efficient protection against UV radiation.