Interactions of tyrosine and tyramine with nucleic acids and their components: Fluorescence, nuclear magnetic resonance and circular dichroism studies

Abstract

Interactions between tyrosine or tyramine and DNA, poly(A), nucleosides or nucleotides have been investigated by fluorescence, proton magnetic resonance and circular dichroism. 1. 1. In frozen aqueous solutions at 77°K, the fluorescence of tyrosine and tyramine is quenched upon interaction with purine or pyrimidine derivatives. The fluorescence of pyrimidines is much more affected than that of purines. 2. 2. In aqueous solutions at room temperature, the PMR signals of the purine and pyrimidine rings are shifted upfield in the presence of tyramine. The PMR signals of tyramine are also shifted to higher fields in the presence of purine derivatives. These PMR results demonstrate that complex formation in aqueous solutions involves a stacking of the aromatic rings of both molecules. 3. 3. Tyramine interacts with native double-stranded DNA. The fluorescence of tyramine is quenched in the complex and the circular dichroism spectrum of DNA is affected by the binding of tyramine. A binding constant of approx. 10 3 M −1 has been determined from a study of the competition between serotonin and tyramine for binding to DNA. Electrostatic contribution to the binding process is demonstrated by its dependence upon ionic strength. 4. 4. Tyramine binds to single-stranded poly(A) at pH 7. Circular dichroism and PMR studies indicate that the interactions between the adenine rings in poly(A) are decreased upon binding of tyramine. The proton resonance signals of tyramine are shifted upfield in the presence of poly(A), indicating that the phenol ring of tyramine is stacked with the adenine rings of poly(A). These results are discussed with respect to the role that could be played by tyrosine residues in enzymes or proteins in their interaction with nucleic acids. A direct interaction with the bases is suggested and conformational changes of the nucleic acid are expected as a result of such an interaction.