Comparison of the Metal Ion Promoted Dephosphorylation of Adenosine 5'-triphosphate and Uridine 5'-triphosphate

The dephosphorylation of ATP and UTP in dependence on pH proceeds for both nucleoside 5'-triphosphates (NTP) with the same rate indicating that the nucleic base moieties have no influence on this reaction. This is different in the presence of Cu2+ which promotes the scission of the terminal y phosphate group with both NTP5, but with ATP the reaction is considerably more facilitated. Evidence is given that in the Cu2-ATP systems the base moiety is involved in the reaction, while UTP shows the properties of a simple organic triphosphate (R-TP), like methyltriphosphate, and for these the most reactive intermediate is a Cu2 (R-TP) (OH) complex. This result contrasts with that for the Cu2-ATP system: here the reaction proceeds via a [Cu2(ATP)]2(OH)T,22 dimer. The structures of both reactive intermediates are discussed and compared; reference to other NTP-metal ion systems is made, and some possible implications regarding enzymic systems are indicated.