Complex formation of rutin and quercetin with copper alters the mode of inhibition of ribonuclease A

Rutin and quercetin, both minor components of green tea and their Cu(II) complexes interact with Ribonuclease A (RNase A) in a novel way. The effects of rutin, quercetin and their copper complexes on the catalytic activity of the protein were investigated. Rutin shows an enhancement in the ribonucleolytic activity whereas the copper complexes and quercetin behave as non-competitive type inhibitors with K(i) values in the μM range. The secondary structural changes of RNase A in presence of the ligands were measured by circular dichroism and Fourier transform infrared spectroscopy. The binding parameters were obtained using a fluorescence quenching analysis.