title: Search for extraterrestrial life using chiral molecules: mandelate racemase as a test case.
abstract: We have investigated an enzymatic racemization reaction as a marker for extraterrestrial life, which resulted in a change in optical rotation of a mandelic acid over time, as measured by polarimetry. Mandelate racemase was active in aqueous buffer in a temperature range between 0 degrees C and 70 degrees C and also in concentrated ammonium salt solutions and water-in-oil microemulsions in a temperature range between -30 degrees C and 60-70 degrees C; however, the enzyme was not active in several organic cryosolvents. Thus, we have demonstrated that concentrated ammonium salt solutions and water-in-oil microemulsions, both of which are able to form on extraterrestrial planets and moons in the presence of liquid water, are suitable media for enzyme reactions at subzero temperatures. Kinetic data for the mandelate racemase reaction obtained by polarimetry, while reproducible and internally consistent, differed significantly from several sets of data obtained previously by other methods such as chromatography and hydrogen-deuterium exchange. However, we conclude that reactions yielding a polarimetric signal, such as the racemizations employed in this work, are suitable mechanisms by which to utilize a change in chirality over time as a tool to detect signs of life.
authors.affiliation: School of Chemistry, Georgia Institute of Technology, Atlanta, Georgia 30332-0363, USA.
authors.forename: Tracey L
authors.initials: TL
authors.lastname: Thaler
authors.forename: Phillip R
authors.initials: PR
authors.lastname: Gibbs
authors.forename: Rick P
authors.initials: RP
authors.lastname: Trebino
authors.forename: Andreas S
authors.initials: AS
authors.lastname: Bommarius
mesh_terms: D002021:Buffers; D002152:Calorimetry, Differential Scanning; D004655:Emulsions / Q000737:chemistry; D018559:Exobiology; D005118:Extraterrestrial Environment; D007700:Kinetics; D016958:Pseudomonas putida / Q000201:enzymology / Q000378:metabolism; D019998:Racemases and Epimerases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D013237:Stereoisomerism; D013696:Temperature
chemical_list: D002021:Buffers; D004655:Emulsions; D019998:Racemases and Epimerases; C021540:mandelate racemase