摘要：

Paramagnetic broadening of the proton magnetic resonance peaks of adenine nucleotides is used to determine Cu(II) binding sites, and their relation to molecular conformation. The resonance peaks of adenine protons are broadened by Cu(II) ions as follows: H-8 is broadened preferentially to H-2 in 3′-AMP, 5′-AMP, and poly(A); H-8 and H-2 are broadened equally in adenosine, 2′-AMP, cyclic 3′:5′-AMP, and cyclic 2′:3′-AMP. In tubercidin (7-deazaadenosine), H-2 is broadened preferentially to H-8. These data indicate that proton magnetic resonance broadening is useful in determining the binding site of metal ions on the adenine moiety; electronic changes produced in regions of the ring system remote from the metal binding site do not obfuscate the re-suits, nor does copper binding to phosphate account for broadening of the base peaks. In general, Cu(II) ions can bind to multiple sites on the adenine base, with preference for a given site influenced by molecular associations which in the different AMP isomers is governed by the position of the phosphate on the ribose. The results obtained with 3′- and 5′-AMP can be interpreted by a binuclear 2:2 Cu-AMP complex in which the two bases are stacked with each Cu(II) bound to a phosphate of one AMP and N-7 of the other. The results obtained with 2′-AMP can be interpreted by a chelate involving N-3 and a phosphate group of the same molecule. N-7 is the preferred binding site of Cu(II) in poly(A). Broadening of ribose peaks is in line with these structures.

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