A possible prebiotic function of cytosine as amino acid synthesizer

The biochemical role of pu- rine and pyrimidine bases may have been very different at the beginning of life. Their possible direct involvement in amino acid synthesis was examined via development of an in vitro reaction system, which simu- lated the chemical constituency of early life microenvironments. Reductive amination of pyruvate to alanine and possible alanine products by free cytosine was detected in this system. Crucial to the success of the reaction was an imine formation step, carried out under anhydrous conditions. A similar role for the adenine/hypoxanthine couple could not be verified. The possible evolutionary precedence of such an imine- involving mechanism for direct amino acid synthesis to the appearance of nucleic acids as 'genetic information conveyors' is proposed. INTRODUCTION It is generally believed that life first appeared in a very hot, acidic, reducing, anaerobic, aqueous environ- ment rich in hydrogen gas and sulfur and iron compounds of very negative oxido- reduction potential 1-3 . Free nucleic acid