First-order rate constants (50 'C; I = 0.1 M, NaC10,) for the dephosphorylation of UTP and TTP (1 mM) 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" or Zn2+ (NTP :MZ + = 1 : I ) this changes drastically : ATP-M'+% UTP-M'+z TTP-M'+z CTP-M'+>NTP, the Cuz+ systems being always more reactive than the Zn" systems, and these more than the Ni2+ systems. An interaction between the nucleic base and metal ion is important for the Cu'+-ATP and Zn2+-ATP systems, but not for the pyrimidine-nucleotide systems (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)'-, strongly reduces the activity and all four ternary Cu2+ systems now show the same dephosphorylation rate. Addition of a second equivalent of Cu'+ to the CuZ+-UTP 1 :I 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, uo =d[PO:-]/dt, and the concentration of Cu'+-UTP in 1:l and 2 : l systems was determined. The results suggest that the reactive complex with pyrimidine nucleotides is a monomeric, dinuclear species of the type M,(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-phosphorylations to HzO, and related reactions in viuo are discussed.The enzyme-catalyzed transfers of phosphoryl or nucleotidyl groups depend on the presence of divalent metal ions [2]. Consequently, the various stages of information transfer in genetic processes, DNA replication, RNA synthesis, and protein synthesis all require metal ions also [3,4]. Thus, it is not surprising that metal-ion -nucleotide interactions, especially of nucleoside 5'-triphosphates, are receiving much attention.Of all nucleoside 5'-triphosphates (NTP), the interactions between ATP (see Chart) and metal ions are the best studied [5]. It is known that different metal ions promote the selfassociation differently [6] ; the ' extent of macrochelate formation in the monomeric complexes by the coordination of a metal ion to the phosphate chain and to N-7 is also different [6]. All this is reflected in the varying effectiveness of metal ions in promoting the dephosphorylation of ATP [ 1,7]. This is Part VII of the series Hydrolysis of Nucleoside Phosphutes. Part VI appeared elsewhere [I].Abbreuiutions. Bpy, 2,2'-bipyridyl; M z + , bivalent metal ion; MTP, methyltriphosphate; NTP, nucleoside 5'-triphosphate, i.e. ATP, CTP, GTP, ITP, TTP and/or UTP; (NTP-H), TTP or UTP deprotonated at N-3.The phosphate groups in NTP are labelled as M, /r and y , where the latter refers to the terminal phosphate group. If nothing else is specified, the formula PO:-represents all related species which may be pres...