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
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Media type:
E-Article
Title:
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
Contributor:
SIGEL, Helmut;
HOFSTETTER, Fritz
Published:
Wiley, 1983
Published in:
European Journal of Biochemistry, 132 (1983) 3, Seite 569-577
Description:
First‐order rate constants (50°C; I= 0.1 M, NaClO4) 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 Cu2+ or Zn2+(NTP:M2+= 1:1) this changes drastically: ATP‐M2+≫ UTP‐M2+∼ TTP=M2+°CTP‐M2+ > NTP, the Cu2+ ystems being always more reactive than the Zn2+ systems, and these more than the Ni2+ systems. An interafction between the nucleic base and metal ion is important for the Cu2+ ‐ATP and Zn2+ ‐ATP systems, but not for the pyrimidine‐nucleotide systms (these behave like methyltriphosphate). Accordingly, prevention of the Cu2+ ‐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 Cu2+ systems now show the same dephosphorylation rate. Addition of a second equivalent of Cu2+ to the Cu2+ ‐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, vo= d[PO43−].dt, and the concentration of Cu2+ ‐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 M2(NTP)(OH)− (its formation is inhibited by ligands like tryptophanate), while with M2+ ‐ATP the reactive complex is a dimer. The connection between the indicated dephosphorylations in vitro, i.e. trans‐phosphorylatins to H2O, and related reactions in vivo are discusse.