Tyrosinase inhibitory mechanism of betulinic acid from Dillenia indica

- Tyrosinase inhibition assay guided isolation of betulinic acid from D. indica fruits.
- Enzyme inhibition kinetic analysis reveals its non-competitive inhibition type.
- Betulinic acid binding did not alter the tertiary structure of tyrosinase.
- α-Helix content of the secondary structure of the tyrosinase altered due to ligand binding.
- In-silico analysis explored its expected binding region on the active site of tyrosinase.

The fruit of Dillenia indica L. is extensively used as a food additive. Betulinic acid (BA) is the most prominent secondary metabolite present in D. indica. This study screened the bioassay guided isolation of BA from D. indica and explored its tyrosinase inhibitory mechanism. Half maximal inhibitory concentration (IC50) of BA were calculated as 13.93 µM and 25.66 µM for diphenolase and monophenolase. Enzyme kinetic analysis revealed that BA inhibited tyrosinase activity non-competitively. Further, conformational analysis of tyrosinase with BA was measured by fluorescence and circular dichroism spectroscopy. These results implied that diminish rigidity of enzyme might disturb the catalytic conformation of tyrosinase. Moreover, In-silico analysis confirmed probable binding polar and non-polar region on the active site of tyrosinase. Based on these findings, we suggest that BA from D. indica may be useful in preventing enzymatic browning reactions in food products.