Abstract
Bioassay-guided isolation from
(Theaceae) and
(Liliaceae) utilizing an in vitro model of protease assay revealed colchicine (
) and caffeine (2) from chloroform fractions, respectively. Their structures were validated using spectral techniques. The purified compounds were further optimized with Gaussian software utilizing the B3LYP functional and 6-31G(d,p) basis set. The result files were utilized to determine several global reactivity characteristics to explain the diverse behavior of the compounds. Colchicine (
) showed a higher inhibition of protease activity (63.7 ± 0.5 %age with IC
= 0.83 ± 0.07 mM), compared with caffeine (
) (39.2 ± 1.3 %age). In order to determine the type of inhibition, compound
was further studied, and, based on Lineweaver-Burk/Dixon plots and their secondary replots, it was depicted that compound
was a non-competitive inhibitor of this enzyme, with a Ki value of 0.690 ± 0.09 mM. To elucidate the theoretical features of protease inhibition, molecular docking studies were performed against serine protease (PDB #1S0Q), which demonstrated that compound
had a strong interaction with the different amino acid residues located on the active site of this understudied enzyme, with a high docking score of 16.2 kcal/mol.