Exploration of surface plasmon resonance for yam tyrosinase characterization

Tyrosinase is a ubiquitous enzyme in nature. It catalyzes the reaction in melanin formation. In this investigation, tyrosinase from a Yam tuber (Amorphophallus paeoniifolius) was extracted and purified by ultra-centrifugal filtration followed by ion exchange chromatography. The purified enzyme was obtained with purification fold of 12.65 and specific activity of 60.25 U/mg. The molecular weight of purified enzyme was confirmed to be 45 kDa by SDS-PAGE. The enzyme activity was optimal at pH 6 and 30 °C with Km 10 mM. Further the kinetic study of purified yam tyrosinase was carried out using Surface Plasmon Resonance method. In brief, enzyme was immobilized on chip surface by amine coupling method and different small molecules were analyzed for their binding affinities at different concentrations (mM). The affinity of each compound for yam tyrosinase was different with K_D values as tannic acid (5.13 × 10^-5), gallic acid (2.05 × 10^-8), ascorbic acid (0.004544), caffeic acid (3.09 × 10^-9), pyrogallol (2.13 × 10^-4) and catechol (1.09 × 10^-4). The kinetics data results were confirmed by inhibition assays and IC₅₀ values were calculated. This data will help to study the role of tyrosinase in hyperpigmentation which will create an avenue for tyrosinase inhibitors. Tyrosinase inhibitors have wide range of applications in cosmetics, medical and food industries.