Free radical-induced fragmentation of proteins by quercetin

The flavonoid, quercetin, is known to bind to DNA and, in the presence of Cu(II) and other ions, causes fragmentation of the molecule. We examined whether quercetin might bind to protein and cause similar fragmentation. By using UV spectroscopic and fluorescence quenching experiments we show that quercetin binds to bovine serum albumin and that the complex does, in the presence of Cu(II), lead to fragmentation of the protein. The binding involves binding to tryptophan residues in the albumin. The reaction is not detected in certain other tryptophan-containing proteins. We discuss the possible implications for protein damage by this and other radical-generating reagents.