Metal ions that promote the hydrolysis of nucleoside phosphoesters do not enhance intramolecular phosphate migration

The effects of several metal ions and metal ion complexes on the hydrolysis and interconversion of uridylyl(2′,5′)uridine and its 3′,5′‐isomer were studied as a function of pH and metal ion concentration. The hydrolysis was shown to be markedly accelerated by Zn 2+ , Cd 2+ and trivalent lanthanide ions and by tri‐ and tetraaza complexes of Zn 2+ . In contrast, none of these species appreciably promotes the interconversion of the 2′,5′‐ and 3′,5′‐isomers, in spite of the fact that this reaction proceeds through the same pentacoordinated intermediate as the hydrolysis. Lanthanide ions also promote the hydrolytic dephosphorylation of uridine 2′‐ and 3′‐monophosphates, but have a barely noticeable effect on their interconversion. The mechanisms of the metal ion‐promoted reactions are discussed.