Adenosine and Inosine 5′‐triphosphates

Abstract

The chemical shift of the protons, H(2) and H(8), in the proton magnetic resonance spectra of ATP, ITP, and inosine was measured in aqueous solution in dependence on pH (2 to 12). Based on these data the sites of protonation or deprotonation are identified and the acidity constants determined. A comparison of the constants due to the nucleotides with the corresponding ones of the nucleosides evidences that the basicity of the nucleic base increases somewhat under the influence of the triphosphate chain. The possibility of an intramolecular hydrogen bound between N(7) and the proton of the y-phosphate group is discussed.From the line broadening effects in the presence of Cu2+ it is concluded that this metal ion interacts mainly with N(7) of ATP, but with the N(l), 0 (6) is nearly completely formed) reveal the surprising fact that in the pH range 2 to 6 the line broadening of the signal due to H(8), and H(2) as well, increases signiticantly compared with a system containing only ITP and Cua+. This observation is easily explained by the assumption of a chargetransfer interaction within the ternary complex, Cu(Bipy) (ITP)2-, i.e. between the purine part of the nucleotide and 2,2'-bipyridyl. This interaction could indeed be contirmed by spectrophotometric measurements in the ultraviolet (Amax = 313 nm). Similar results were obtained for the mixed-ligand complex, Cu(Bipy) (ATP)2-. The distance between the planes of the aromatic rings in these systems is estimated and a structure for these metal-ion-bridged charge-transfer complexes is suggested. The biological implications of such ternary, metal-ion-bridged, charge-transfer complexes are briefly indicated.Recent studies on the dephosphorylation of the binary and ternary complexes, CU(ATP)~-and Cu(Bipy)(ATP)2- [3,4], and the extension of this work to other nucleotide complexes (H. Sigel, D. H. Buisson and B. Prijs, unpublished results) prompted us to investigate the coordination behavior of ITP in mixed-ligand complexes. For reasons of comparison inosine and ATP were included' in this work. From earlier studies on binary complexes [6,6] it is known that Cu2+ coordinates to the j3-and y-phosphate groups of ATP4-as well as to N(7) of the adenine moiety, and thus a macrochelate is formed [6, 71, which is crucial indeed for the Cu2+-accelerated dephosphorylation of ATP [2,4,7]. Unfortunately, the coordination behavior of ITP is less clear cut. However, as the N(7); usually the latter two are favored.In solution, Cu2+ prefers a square-planar (or grossly distorted) coordination sphere [13,14] ; hence, in Cu(Bipy)2+ only two positions remain available for the binding of a second ligand [la], the coordination of which results in a ternary complex. In fact, for Cu(Bipy)(ATP)2-it was shown by means of proton magnetic resonance (PMR) that in this mixedligand complex the adenine moiety does not interact any more with Cu2+ [16]. It is believed that this is Eur. J. Biochem. 41 (1974)

Complex Formation of Cadmium with Sugar Residues, Nucleobases, Phosphates, Nucleotides, and Nucleic Acids

“…Originally the interactions had been proven by UV spectrophotometry [217][218][219][220] and 1 H NMR shift measurements [201,222,223]. Later, complexes of the type M(Arm)(adenine nucleotide)…”

“…About 40 years ago intramolecular aromatic-ring stacking was described for the first time [217,218] between heteroaromatic N bases (Arm), i.e., 2,2'-bipyridine or 1,10-phenanthroline, and AMP 2-, ADP 3-or ATP 4-, both ligands being bridged by a metal ion [200,[219][220][221].…”

A Comparison on the Coordination Tendency towards Cu2+ of the Base Moieties in Guanosine, Inosine and Adenosine 5′‐Triphosphates

“…The desired pH of a solution was adjusted by using a glass stick and dotting with solutions of concentrated HC104 or NaOH. The exact experimental conditions are given in the legends to the figures, and further details have recently been described [8]. Using water as a solvent, which has the advantage of a well-defined pH scale, we first recorded spectra of pure GTP solutions over a large pH range.…”

“…4 it is shown that Cuz+ coordinates to N (7) with all three purine-nucleoside 5'-monophosphates, i. e. AMP, GMP and IMP. Molecular models suggest that the different behavior of the metal ion in Cu(1MP) 191 and Cu(1TP)Z- [8] is due to steric reasons: in Cu(1TP)'-the metal ion, already bound to the phosphate chain, reaches easily the N(1), O(6)-site, while this appears impossible in Cu(1MP). Graphical determination of the acidity constant, Kay for the depronow studied the coordination tendency of the purine moiety in GTP4-toward Cu2+, and indeed, it turned out that this is more similar to the one of ATP4-than to that of ITP4-.…”

“…The chemical shift of the proton H (8) in the proton magnetic resonance spectrum of GTP was measured in aqueous solution in dependence on pH (2 to 12). Based hereon the acidity constants for protonation at N(7) and deprotonation at N( 1) were determined.…”