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Updated: Sep 26, 2025

Conducting Miller-Urey Experiments
Published on: January 21, 2014
Did Homocysteine Take Part in the Start of the Synthesis of Peptides on the Early Earth?
Sparta Youssef-Saliba1, Anne Milet1, Yannick Vallée1
1University Grenoble Alpes, CNRS, DCM, F-38058 Grenoble, France.
Abstract:
Unlike its shorter analog, cysteine, and its methylated derivative, methionine, homocysteine is not today a proteinogenic amino acid. However, this thiol containing amino acid is capable of forming an activated species intramolecularly. Its thiolactone could have made it an interesting molecular building block at the origin of life on Earth. Here we study the cyclization of homocysteine in water and show theoretically and experimentally that in an acidic medium the proportion of thiolactone is significant. This thiolactone easily reacts with amino acids to form dipeptides. We envision that these reactions may help interpret why a methionine residue is introduced at the start of all protein synthesis.
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