HR: 17:45h
AN: B52F-08 INVITED     [PDF]
TI: Amino Acid Enantiomeric Ratios in Biogeochemistry: Complications and Opportunities
AU: * McDonald, G D
EM: Gene.D.McDonald@jpl.nasa.gov
AF: Jet Propulsion Laboratory, MS 183-301 4800 Oak Grove Drive, Pasadena, CA 91109 United States
AU: Sun, H J
EM: Henry.Sun@jpl.nasa.gov
AF: Jet Propulsion Laboratory, MS 183-301 4800 Oak Grove Drive, Pasadena, CA 91109 United States
AU: Tsapin, A I
EM: tsapin@jpl.nasa.gov
AF: Jet Propulsion Laboratory, MS 183-301 4800 Oak Grove Drive, Pasadena, CA 91109 United States
AB: Amino acid enantiomeric ratios have been used for many years as an indicator of the process of racemization, and thus as a method to determine the age of biological samples such as bones, shells, and teeth. Dating biological samples by this method relies on an accurate knowledge of the environmental temperatures the sample has experienced, and the racemization kinetic parameters in the sample matrix. In some environments, where an independent dating method such as radiocarbon is available, the observed amino acid D/L ratios are found to be either higher or lower than those expected due to racemization alone. The observed D/L ratios in these cases can be clues to biogeochemical processes operating in addition to, or in place of, chemical racemization. In Siberian permafrost (Brinton et al. 2002, Astrobiology 2, 77) we have found D/L ratios lower than expected, which we have interpreted as evidence for low-level D-amino acid metabolism and recycling in microorganisms previously thought to be metabolically dormant. In microbially-colonized Antarctic Dry Valley sandstones (McDonald and Sun 2002, Eos Trans. AGU 83, Fall Meet. Suppl., Abstract B11A-0720) we have found D/L ratios higher than can be accounted for by racemization alone, most likely due to the accumulation of D-amino-acid-containing peptidoglycan material from multiple bacterial generations. D/L profiles in polar ices and in ice-covered lakes (Tsapin et al. 2002, Astrobiology 2, 632) can be used to indicate the sources and histories of water or ice samples. Multiple biological and biogeochemical processes may complicate the interpretation of amino acid enantiomeric excesses in both terrestrial and extraterrestrial samples; however, amino acid racemization remains a useful tool in biogeochemistry and astrobiology. With a good knowledge of the environmental history of samples, amino acid D/L profiles can be used as a window into processes such as molecular repair and biomass turnover that are difficult to detect by other means, particularly over geological time scales.
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2003 Fall Meeting