Molecular interaction of L-tryptophan with bases, ribonucleosides and DNA.

The interaction of L-aromatic aminoacids with bases and nucleosides is described. Of these, L-tryptophan interacts more strongly with bases and nucleosides as indicated by nuclear magnetic resonance, circular dichroism and solubility measurements. A possible ring-ring type interaction between the aminoacid and bases or nucleosides is proposed; this interaction being such that the hydrodinamic behaviour of the DNA molecule is unchanged. Ultra violet irradiated DNA is protected by L-tryptophan. A mechanism of energy transfer from the DNA to tryptophan trough triplet-triplet states is discussed.