Self-association of 1,N6-ethenoadenosine 5'-triphosphate (epsilon-ATP) and promotion by metal ions.
The concentration dependence of the chemical shifts of the protons H-2, H-8, H-10, H-11, and H-1' of 1,N6-ethenoadenosine 5'-triphosphate (epsilon-ATP4-) has been measured in D2O at 27 degrees C to elucidate the self-association. The results are consistent with the isodesmic model of indefinite noncooperative stacking; the association constant, K = 1.9 +/- 0.2 M-1, is only slightly larger than the value for ATP4-, K = 1.3 +/- 0.2 M-1. The self-stacking tendency of epsilon-ATP4- is promoted by a factor of about 4 by (1:1) coordination of Mg2+ to the phosphate moieties, which probably links these together and also neutralizes part of the negative charge; Zn2+ is only about half as effective as Mg2+ in promoting the self-association. This result contrasts with the self-stacking properties of Mg(ATP)2- and Zn(ATP)2-, Zn2+ being considerably more effective in a 1:1 ATP system. It is assumed that due to the enhanced affinity of the N-6/N-7 site of the epsilon-adenine moiety towards Zn2+ repulsion of the bases occurs resulting thus in a lower stacking tendency; in addition, the simple isodesmic model is no longer applicable to the Zn(epsilon-ATP)2- system: to explain the experimental data, the formation of an intermolecular metal ion bridge in the dimeric stacks is proposed. The experimental conditions required for studies of the properties of monomeric epsilon-ATP systems are described. Care should be exercised in employing epsilon-ATP as a probe for ATP.
K H
KH
Scheller
H
H
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D000255:Adenosine Triphosphate / Q000031:analogs & derivatives*; D004985:Ethenoadenosine Triphosphate / Q000378:metabolism*; D046911:Macromolecular Substances; D008274:Magnesium / Q000378:metabolism*; D008433:Mathematics; D011108:Polymers / Q000378:metabolism; D015032:Zinc / Q000378:metabolism*
D004985:Ethenoadenosine Triphosphate; D046911:Macromolecular Substances; D011108:Polymers; D000255:Adenosine Triphosphate; D008274:Magnesium; D015032:Zinc