Metal‐Ion‐Promoted Dephosphorylation of the 5′ ‐Triphosphates of Uridine and Thymidine, and a Comparison with the Reactivity in the Corresponding Cytidine and Adenosine Nucleotide Systems

First‐order rate constants (50°C; I = 0.1 M, NaClO 4 ) for the dephosphorylation of UTP and TTP (1mM) in the pH range 2—10 are compared with those of ATP and CTP; they all show the same properties indicating that the nucleic base has no influence on the rate. In the presence of Cu 2+ or Zn 2+ (NTP:M 2+ = 1:1) this changes drastically: ATP‐M 2+ ≫ UTP‐M 2+ ∼ TTP=M 2+ °CTP‐M 2+ > NTP, the Cu 2+ ystems being always more reactive than the Zn 2+ systems, and these more than the Ni 2+ systems. An interafction between the nucleic base and metal ion is important for the Cu 2+ ‐ATP and Zn 2+ ‐ATP systems, but not for the pyrimidine‐nucleotide systms (these behave like methyltriphosphate). Accordingly, prevention of the Cu 2+ ‐purine interaction by the addition of one equivalent of 2,2′ ‐bipyridyl, leading to Cu((Bpy) (NTP) 2− , strongly reduces the activity and all four ternary Cu 2+ systems now show the same dephosphorylation rate. Addition of a second equivalent of Cu 2+ to the Cu 2+ ‐UTP 1:1 system enhances the dephosphorylation rate significantly and Job's method provides evidence that a 2:1 complex is the most reactive intermediate. The relation between the initial rate, v o = d[PO 4 3− ].d t , and the concentration of Cu 2+ ‐UTP in 1:1 and 2:1 systems was determined. The results suggest that the reactive complex with pyrimidine nucleuotides is a monomeric, dinuclear species of the type M 2 (NTP)(OH) − (its formation is inhibited by ligands like tryptophanate), while with M 2+ ‐ATP the reactive complex is a dimer. The connection between the indicated dephosphorylations in vitro , i.e. trans ‐phosphorylatins to H 2 O, and related reactions in vivo are discusse.