Formation of amide bonds without a condensation agent and implications for origin of life

Amide bonds are of central importance for biochemistry; in the guise of peptide bonds, they form the backbone of proteins. The formation of amide bonds without the assistance of enzymes poses a major challenge for theories of the origin of life. Enzyme-free formation of amide bonds between amino acids has been demonstrated in the presence of condensing agents such as cyanamide. Here we report the formation of amide bonds in aqueous solution in the absence of any condensing agent. We find that the formation of pyrite (FeS2) from FeS and H2S can provide the driving force for reductive acetylation of amino acids with mercaptoacetic acid (HSCH2COOH). The redox energy of pyrite formation permits the activation of the carboxylic acid group, which is converted to a species that reacts readily with amines. This process provides support for the chemo-autotrophic theory for the origin of life, in which pyrite formation supplies the energy source for the first autocatalytic reproduction cycle.