Volcano gas, amino acids make peptides

In an experiment that closely simulated conditions likely to have been present in the primitive Earth, bubbling simple volcanic gas into a solution containing amino acids brought about the formation of peptides, according to a study published this week in Science. The study, critics agree, is a major step forward in deciphering the chemistry of the transformation of monomers into polymers in the early Earth.Luke Leman, of the Scripps Research Institute, and his colleagues added carbonyl sulfide into air-free aqueous solutions that contained L-phenylalanine, and obtained dipeptides and tripeptides in yields of up to 80% at room temperature. Mixtures of other amino acids combined into peptides as well.Amino acids, and other monomers, can be obtained under prebiotic experimental conditions, and have also been found in meteorites, comets, and interplanetary dust particles hitting the Earth, said M. Reza Gadhiri, also from Scripps, and a co-author of the paper. "We have the monomers, the question is how to put them together into peptides." The authors suggest that carbonyl sulfide helped form peptides in localized aquatic environments close to volcanic eruptions in the prebiotic Earth.This is not the first time that peptides are synthesized in the laboratory. But, according to Leslie Orgel, of the Salk Institute for Biological Studies, another author of the paper, the reagents used up to now had been much less efficient than carbonyl sulfide at making peptides. More importantly, no one is certain that the reagents previously used were even present on the primitive Earth. "But there is absolutely no reason to believe that carbonyl sulfide, which comes out of volcanoes today, hadn't come out of volcanoes 4 billion years ago, or roughly, when life was beginning," He said. George Cody, at the Carnegie Institution in Washington, who did not participate in the research, said that "the authors have done a spectacular job in mapping up the chemistry and showing precisely what the mechanism is. To form biopolymers you usually have to activate the monomers with chemical groups that are very unrealistic for a prebiotic scenario."In the reactions described in this paper, carbonyl sulfide combines with free amino acids to form an activated compound that soon goes through a condensation-dehydration reaction leading to peptides. For Cody, the fact that the reactions occurred in an aqueous solution is also critical. "It's easy to condense peptides in polar and anhydrous (free from water) solutions, but not under these conditions," he told The Scientist.Jeffrey L. Bada, of the Scripps Institution of Oceanography, who was not involved in the research, praised the fact that the experiments were conducted at ambient temperatures. "One of the things I have objected to very strongly about papers describing reactions at high temperatures [and proposing a hydrothermal scenario for the formation of polymers] is that if those reactions occur at 100°C, they also should occur at lower temperatures." He also drew attention to the fact that the yields of peptides reported in this paper are far greater than what other authors have found at 100°C. "This is a very robust reaction." Bada said that there has been a "fascination with hydrothermal systems" ever since they were discovered some twenty years ago. "People have sort of got this idea that somehow these things are important in prebiotic chemistry," he said.To Orgel, however, the temperature was not what was relevant in his experiments. "No one knows the temperatures on Earth when life begun," he said. "My guess would be that there was a low temperature, other people's guess is that there was a high temperature. Orgel said that the researchers were not claiming to have found a solution for the problem of the origin of life. "This is one little piece of the problem, which is not even solved," he said. "It's a suggestion towards the solution."Correction (posted October 12, 2004): When originally posted, this story had an erroneous headline suggesting that the experiment described created life. The experiment created peptides. The Scientist regrets the error.

Volcano gas, amino acids make peptides

Study is important in understanding transformation of monomers into polymers

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