HAVE ADENOSINE 5'-TRIPHOSPHATE (ATP4-) AND RELATED PURINE-NUCLEOTIDES PLAYED A ROLE IN EARLY EVOLUTION - ATP, ITS OWN ENZYME IN METAL-ION FACILITATED HYDROLYSIS

Had ATP a directing role in early evolution? Mechanistic studies on the in vitro dephosphorylation of adenosine 5'-triphosphate (ATP-) revealed that in the presence of metal ions (M2+), like Zn2+, Cd2+ or Cu2+ the reaction proceeds via dimeric species, i.e. preferably via [M2(ATP)]2(OH)- or [M2(ATP)]2 depending on pH. These dimers occur in low concentration and involve purine stacking and a M2+/N-7 interaction. In other triphosphate monoesters with a non-coordinating organic residue including pyrimidine-nucleoside 5'-triphosphates, which are considerably less reactive than the ATP systems, monomeric species govern the reactivity. The reason for the high reactivity of the M2+/ATP dimers is that one of the two ATPs takes over a structuring role and thus ATP acts as its own hydrolytic 'enzyme'. It is noticeable that this structuring role can also be adopted by purine-nucleoside 5'-monophosphates, AMP- being especially effective. Based on these observations it is suggested that ATP may have played a directing role in early evolution, i.e. in a primitive metabolism without genetics. To say it differently, due to its self-activating properties ATP might have been able to stick out of the chemical 'noise' present on the early earth. In this way ATP might have participated in paving the way for a genetically based 'RNA World'. The role of Mg2+ and other metal ions as well as that of adenosine 5'-diphosphate (ADP) and of other purine-nucleotides is also discussed.