| Abstract | This ¹H nmr study provides the first experimental evidence for specific complex formation between the coenzyme nicotinamide adenine dinucleotide (β-NAD⁺) and the two aromatic amino acids phenylalanine and tryptophan. It is shown that the interaction is of the stacking type and occurs between the aromatic side chains of these amino acids and the adenine moiety of NAD⁺. Binding parameters were obtained from dilution studies, taking into account the self-association of NAD⁺. The apparent microscopic association constants for complex formation of phenylalanine and tryptophan with excess NAD+ in aqueous solutions are 1.35 M⁻¹ and 11.35 M⁻¹, respectively, indicating that the adenine moiety of NAD⁺ can discriminate between phenylalanine and tryptophan by a stronger binding to the latter. The results are discussed with regard to the interaction of NAD⁺ with dehydrogenases. |
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