Stacking interactions between aromatic amino acids and adenine ring of ATP in zinc mediated ternary complexes

Spectrophotometric studies have provided evidence for zinc-mediated ternary complexes between ATP and aromatic amino acids. The hypochromicity observed in the 260 nm band of ATP increased in the order phenylanine <tyrosine<tryptophan. Adding alanine did not produce any change of the ATP spectrum. The association constant was four fold higher for the ATP-Zinc-Tryptophan complex than for that of the ATP-Zinc-Alanine. The increased stability of the former complex was ascribed to the stacking interaction between indole and adenine rings. The maximum concentrations of the ATP-Zinc-Tryptophan complex occurred at about pH 8.0. For these ternary complexes several possible stacked structures involving or not involving N(7) of adenine are discussed.