Adenosine 5'-tetraphospho-5'-adenosine (Ap 4A) plays a role in cellular metabolism in a wide variety of organisms. Because the divalent cations Mg 2+ and Zn 2+ are involved in the synthesis and function of Ap 4A, the effect of divalent cations on the dinucleotide's conformation is of interest. 1H and 31P chemical shift experiments were carried out as a function of Mg 2+ concentration and pH. We propose that Mg 2+ stabilizes the unusual ring-stacked conformation of Ap 4A at pH > 2 by interacting with the β-phosphates. To further probe conformational effects, stable complexes of Ap 4A with Co 3+ were studied using 1H and 31P NMR. Co 3+ forms two different bidentate complexes with Ap 4A, independent of whether the other four octahedral coordination sites are occupied by ammonia or trimethylenediamine. NMR results suggest that in one complex the Co 3+ is coordinated to two β-phosphates and ring stacking is stabilized. In the other complex, Co 3+ is coordinated to an α-phosphate and its neighboring β-phosphate and ring stacking is destabilized. These results further support the hypothesis that Mg 2+ stabilizes the ring-stacked conformation by interacting symmetrically with the two β-phosphate groups.
|Original language||English (US)|
|Number of pages||5|
|Journal||Journal of Biological Chemistry|
|State||Published - 1986|
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