Abstract
The Rubia cordifolia Linn (Manjistha) is a wealthy resource of anthraquinones and its derivatives. In this study, the tyrosinase inhibitory potential of R. cordifolia (root extracts) was explored through bio-activity guided fractionation. Anti-tyrosinase assay guided fractionation led to obtained three different bioactive fractions, e.g., F3, F4 and F5 from plant extract. Subsequent, Liquid chromatographic (RP-HPLC) analysis revealed the active fractions contained 0.89±0.03%, 3.24±0.18% and 2.03±0.24% (w/w) of purpurin respectively. The study indicated that the most bioactive fraction of R. cordifolia (F4) and purpurin showed primarily monophenolase inhibition and to a lesser extent diphenolase inhibitory activity. In addition, results of enzyme kinetic analysis shown F4 and purpurin reversibly inhibited tyrosinase in a competitive manner. 1-Anilino-8-naphthalene sulfonate (ANS)-binding fluorescence measurement proved that conformation of tertiary structure of tyrosinase was not altered by inhibitors. Although circular dichroism (CD) spectroscopy analysis showed that α-helical content of secondary structure decreased with increment of inhibitor's concentration. Molecular docking results implied that the possible inhibitory mechanisms may be attributed to purpurin interaction with copper ion coordinating three histidine residues (HIS61, HIS85, and HIS263) of tyrosinase. This finding could be of importance in prevention of the undesirable enzymatic browning reaction of food products, as well as hyper-pigmentation of human skin.
Published Version
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