A study for the cause of ferulic acid-induced quenching of tyrosine fluorescence and whether it is a reliable marker of intermolecular interactions or not.

Intrinsic fluorescence of peptides and proteins is extensively used to monitor their specific interactions with several natural and synthetic molecules known to have wide-ranging beneficial or detrimental effects on health. A consequence of these interactions would be a significant decrease of the fluorescence emission intensity of Tyrosine (Tyr) and/or Tryptophan (Trp) residues in the protein due to structural rearrangements of proteic microenvironment. However fluorescence quenching can be also caused by "trivial" artefacts. In this study we examined the effect of Ferulic acid (FA) on Tyr fluorescence. FA is a natural anti-oxidant suggested to bind to and to modify the structural properties of several proteins thus altering their biological activities. Fluorescence spectroscopy experiments on Tyr and on proteins containing Tyr and no Trp like beta amyloid peptides and Insulin were performed. Our results suggest that Tyr fluorescence loss can mainly result from an inner filter effect rather than from specific interactions with FA.