Making Peptides on Early Earth

Whether formed on Earth or brought here by meteorites, α-amino acids are widely assumed to have been present in the prebiotic chemical soup. Recent experiments hint at how these amino acids might have been strung together to form peptides.

M. Reza Ghadiri and Luke L. Leman of Scripps Research Institute and Leslie E. Orgel of Salk Institute in San Diego demonstrate that carbonyl sulfide--a volcanic gas believed to be present in the atmosphere of prebiotic Earth--acts as a highly efficient condensing agent for the formation of peptides from amino acids in aqueous solution [Science, 306, 283 (2004)]. Depending on the reaction conditions and additives such as metal ions or oxidizing agents, peptide yields can go up to 80% in minutes to hours at room temperature.

These results suggest this simple, naturally occurring gas may have helped link amino acids into proteins on early Earth, Ghadiri says. "We believe that carbonyl sulfide is the most prebiotically relevant condensing agent yet described, with the possible exception of inorganic polyphosphates," he adds. Because carbonyl sulfide likely didn't last long in the early Earth's atmosphere, he suggests that the gas may have mediated polymerization of amino acids adsorbed to rocks in the vicinity of volcanic eruptions or near carbonyl sulfide-belching underwater vents.