The binding site of Fe3+ in the purine base of adenosine 5'-triphosphate (ATP) was studied by nuclear magnetic resonance (NMR). The NMR relaxation rates (R-1) of H-1 and P-31 in ATP solutions free of and containing ferric ions were measured in the pH range of 3-10. It was found that Fe3+ selectively enhanced the relaxation rate of protons. In the presence of Fe3+, the R-1 of H2 was much bigger than that of H8 at a lower pH (3-4.5), while at a higher pH (5.5-7.5) the R-1 of H8 was more enhanced than H2. At a pH of around 5, both H2 and H8, as well as all three phosphorous, showed a sudden jump ...
