Abstract:The purpose of this study was to investigate the inhibition effect of 4-hydroxycinnamic acid (HCA) on the catalytic activity of tyrosinase on the monophenol substrate L-tyrosine and diphenol substrate L-dopa. The mechanism of inhibition was studied using UV-vis spectroscopy, fluorescence spectroscopy, and molecular docking. The results showed that HCA was more effective at inhibiting the catalytic activity of tyrosinase on the diphenol substrate L-tyrosine than on the monophenol substrate L-dopa; their IC50 values were 0.096 and 0.500 mmol/L, respectively. The UV-visible spectrum showed a red shift in the characteristic absorption peak of HCA because of the formation of a Cu2+ chelate complex. Furthermore, fluorescence quenching of HCA in tyrosinase solution did not occur and instead, the fluorescence intensity increased with increasing HCA concentration, indicating that HCA was catalytically oxidized to the corresponding quinone by tyrosinase. Molecular docking demonstrated that HCA could competitively occupy the positions of both monophenol and diphenol substrates in the active site of tyrosinase by hydrogen bonds and hydrophobic interaction, and could coordinate to Cu2+ in tyrosinase, thus inhibiting the catalytic activity of tyrosinase on L-tyrosine and L-dopa oxidation.
