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Protection of Adenosine 5-Triphosphate toward Hydrolysis by the Formation of a Mixed-Ligand Metal Ion Complex.

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Protection of Adenosine 5‘-Triphosphate
toward Hydrolysis by the Formation of a
Mixed-Ligand Metal Ion Complex‘**]
By David H. Buisson and Helmut Sigel[’]
It is well known that metal ions of the 3d-series enhance
the rate of hydrolysis of adenosine 5’-triphosphate (ATP)
considerably[’, ’I. Cu”, in fact, was shown to be one of
the most effective catalysts[’] and to form-within
the
mentioned series-the most stable binary complex with
ATPC3]. We have now investigated the tendency for
hydrolysis of ATP within a ternary complex.
Studies of mixed-ligand complexes revealed that those
which contain an aromatic arnine and a second ligand with
0 as donor atoms are especially stablef4’’I. This is also true
for 2,2’-bipyridyl(bpy)-Cu’+-phosphate
Indeed, these ternary complexes are even more stable than
the corresponding binary ones. Hence, equilibrium (a)
Cu(ATP)’-
+ Cu(bpy)’+ =+Cu(bpy) (ATP)’-
+CU*+
(a)
is shifted towards the right. (Equilibrium constant :
A log K = log h$$$:i(ATP)- log A$,:
= 6.91 -6.38
= 0.53‘61).
This fact stimulated us to study the rate of the hydrolysis
of ATP in the mixed-ligand complex, Cu(bpy) (ATP)’[probable structure cf. (I)] and compare it with the
corresponding rates for Cu(ATP)’- and free ATP. The
results are shown in Figure 1, where the first order rate
constant ( k ) is plotted against pH. Obviously, the hydrolysis of ATP in the ternary complex is insignificant
compared with that of the binary complex. Moreover, even
free ATP is somewhat more sensitive toward hydrolysis
20
c
10 -
u)
rn
0
5c
‘&I
In other cases Cu(bpy)’+ is a better catalyst than C$I,
e . g . . in the decarboxylation of acetonedi~arboxylate[~]
and
the disproportionation of H202f101.However, in these
cases, the substrate coordinates identically in the binary
and ternary complexes.
[I] P. W. Schneider and H . Brintzinger, Helv. Chim. Acta 47, 1717
(1964).
[2] M . Tetas and J . M. Lowenstein, Biochemistry 2, 350 (1963).
[3] R. PhiNips, Chem. Rev. 1966, 501.
[4] R.Griesserand H . Sige/,Inorg. Chem. 9,1238(1970); 10,2229(1971).
[5] H . Sigel and D.B. MeCorrnick, Accounts Chem. Res. 3, 201 (1970).
[6] H . Sige/, K. Becker, and D. B. MrCormick, Biochim. Biophys. Acta
148,655 (1967).
[7] M . Cohn and T. R. Hughes, Jr., J. Biol. Chem. 237,176 (1962).
[S] A. A. Hirara and D.Applemnn, Analyt. Chem. 31,2097 (1959).
[9] R . W. Hay and K. N . Leong, Chem. Commun. 1967, 800; J. Chem.
SOC.A 1971,3639.
[lo] H . Sigel, C.Flier/, and R . Griesser, J. Amer. Chem SOC.91, 1061
(1969): H Sigd and K . W V S Tunpublished.
.
I
2
The different behavior in the hydrolysis of these binary and
ternary complexes can be rationalized as follows: As Cu2+
prefers a square-planar coordination sphere in aqueous
solution, only two positions are left in Cu(bpy)’+ for the
coordination of ATP, namely by two of its phosphate
groups. Hence, in the mixed-ligand complex, Cu(bpy)
(ATP)’-, the adenine moiety, i.e. N(7), is unable to participate in further complex formation[61 [cf. ( I ) ] . In
contrast it does so in the binary complex, Cu(ATP)’-, by
forming a macrochelate-which
is obviously crucial for
hydrolysis-with
the p- and y-phosphate groups and
N(7)[‘,’].
Received: August 11, 1972 [Z 709 1Ej
German version : Angew Chem. X4.1103 (1972)
15 -
--t
than is ATP in the mixed-ligand complex. This demonstrates unequivocally that ATP is protected toward
hydrolysis by the formation of the ternary complex,
Cu(bpy)(ATP)’- This resuit is of interest with regard to
biological systems, e.g. the transport of hydrolysissensitive phosphates.
60
PH
I
,
65
70
-
Fig. 1. Hydrolysis of A T P in dependence on pH, characterized as the
first order rate constant. (The increasing concentration of phosphate
was measured wrth molybdenum-reagent [S].) The reagent concentrations were each lo-’ M. In the pH range shown the binary complex, Cu(ATP)’-, and the ternary complex, Cu(bpy) (ATP)’-, are
formed to more than 93% and 95%, respectively (computed with the
constants given in Ref. [6]).
[*] Dr. D. H Buisson and Doz. Dr. Helmut Sigel
Institut fur Anorganische Chemie der Universitat
CH-4056 Basel, Spltalstrasse 51 (Switzerland)
[**j The support of this work by the Swiss National Foundation, and a
fellowship to D. H. B. from the University Grants Committee of New
Zealand and from the Educational Department, Basel (Switzerland) is
gratefully acknowledged.
Angew. Chem. internat. Edit. I Val. I 1 (1972) / N o . 11
Structure and Properties of
a,@-DiferrocenylmethyliumIon
By S. Lupan, M. Kapon, Michael Cais, and Frank H .
Herbstein [‘I
The origin of the unusual stabilization of carbenium ions
adjacent to metallocenes has been a matter of vigorous
debate for over a decade“]. Three distinct models have been
[*] S . Lupan. M . Kapon. Prof. Dr. M. Cais. and Prof. Dr. F. H. Herbstein
Department of Chemistry, Israel Institute of Technology,
Haifa (Israel)
1025
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triphosphate, complex, ion, towards, adenosine, metali, protection, formation, mixed, ligand, hydrolysis
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