A Clue for Prebiotic Conversion of Carboxylic Acids and Its Evolutionary Relevance to the TCA Cycle

Abstract

A possibility for the prebiotic conversion of carboxylic acids and the evolutionary onset of a primitive metabolism, which may have served as a medium for the presentday metabolic pathway equipped with enzymes, was examined under submarine hydrothermal environments. We used a flow-reactor system simulating submarine hydrothermal environments for the purpose. It was found that malate, which is one of the TCA cycle member molecules, was synthesized from three other kinds of the member molecules; namely alpha ketoglutarate, succinate and fumarate, in the absence of the relevant enzymes. Furthermore, citrate was synthesized in the solution including pyruvate and all kinds of the TCA cycle member molecules. The synthesis of citrate was significantly suppressed when neither pyruvate nor one of the member molecules was present in the initial setup of the starting reaction solution. These results suggested that submarine hydrothermal environments could have played an important role for the prebiotic conversion and synthesis of carboxylic acids and for the ignition of a primitive metabolism.