Tyrosinase inhibitory effects of Vinca major and its secondary metabolites: Enzyme kinetics and in silico inhibition model of the metabolites validated by pharmacophore modelling

Abstract In the present study, we aimed to identify the tyrosinase enzyme inhibitory potential of Vinca major L. extract and its secondary metabolites. The extract possessed remarkable tyrosinase enzyme inhibitory effect with IC50 value of 20.39 ± 0.44 µg/mL compared to the positive control, kojic acid (IC50 8.56 ± 0.17 µg/mL). Compounds 1 and 5 were the most potent isolates with IC50 values of 32.41 ± 0.99 and 31.34 ± 0.75 µM, they were more potent than kojic acid (IC50: 60.25 ± 0.54 µM). Compound 2 also exhibited remarkable tyrosinase inhibition with an IC50 value of 64.51 ± 1.29 µM. An enzyme kinetics analysis revealed that 1 was a mixed-type, 2 and 5 were noncompetitive inhibitors. Using molecular docking, we predicted binding affinity and interactions of the compounds, which were in good alignment with a pharmacophore hypothesis generated out of a number of known tyrosinase inhibitors. The modelling studies underlined crucial interactions with the copper ions and residues around them such as Asn260, His263, and Met280.