| SUBJECT | Meteorites carrying a preponderance of L-amino acids may have been the original source of nature's handedness. Could these chiral compounds have transferred their asymmetry to other prebiotic molecules, such as sugars? This possibility has now been examined by Sandra Pizzarello, a chemistry professor at Arizona State University, Tempe, and Arthur L. Weber of the SETI Institute, Moffet Field, Calif. They simulated a prebiotic sugar synthesis by reacting glycolaldehyde and formaldehyde in aqueous buffer in the presence of an amino acid catalyst in various enantiomeric excesses [Science, 303, 1151 (2004)]. Two catalysts were tested: isovaline, the most abundant chiral amino acid in meteorites, and alanine, a common amino acid. The reaction produced threose and erythrose, both with enantiomeric excess. The L-amino acids catalyzed the aldol condensation of the aldehyde, affecting the chirality of the sugar products. It is especially likely that isovaline played a role in directing handedness, Pizzarello says, because isovaline does not racemize in water, as do most amino acids and sugars. |
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