A potentiometric and spectrofluorimetric approach to unravel inhibitory effects of semi- and thiosemicarbazones on mushroom tyrosinase activity

The inhibitory efects on mushrooms tyrosinase activity of some semi- and thiosemicarbazones were investigated. While the semicarbazones are inactive, the thiosemicarbazones are, in general, more active than the reference (kojic acid, IC50=70 μM), with maximum activity obtained with benzaldehyde thiosemicarbazone (IC50=7 μM). These inhibitors probably act by coordination of the copper(II) metal ions in the active site of tyrosinase: efectively, potentiometric studies conducted in water solutions confrm that the most active thiosemicarbazone is a good ligand for copper(II) ions. The tyrosinase CD spectra do not show any signifcant diference by addition of an inhibitor or an inactive compound. On the contrary, interesting results were obtained by spectrofuorimetric titrations of mushrooms tyrosinase aqueous solutions with some of the investigated compounds, giving helpful information about possible mechanism of action. The thiosemicarbazones here reported are not cytotoxic on human fbroblasts and do not activate cells in a pro-infammatory way