Tyrosinase covalently immobilized on carboxyl functionalized magnetic nanoparticles for fishing of the enzyme's ligands from Prunellae Spica.

In this study, tyrosinase was immobilized on carboxyl functionalized silica-coated magnetic nanoparticles for the first time to be used for fishing of tyrosinase's ligands present in complex plant extract. The immobilized tyrosinase was characterized by transmission electron microscopy, vibrating sample magnetometry, Fourier transform infrared spectroscopy, thermo-gravimetric analyzer, and atomic force microscopy. The reusability and thermostability of the immobilized tyrosinase were found significantly superior to its free counterpart. Two tyrosinase's ligands, that is, caffeic acid (1) and rosmarinic acid (2), were fished out from extract of the traditional Chinese medicine Prunellae Spica by the immobilized tyrosinase. Compound 1 was found to be an activator of the enzyme with the half maximal effective concentration value of 0.27 ± 0.06 mM, while compound 2 was an inhibitor with the half maximal inhibitory concentration value of 0.14 ± 0.03 mM. Taking advantage of the convenience of magnetic separation and specific extraction ability of ligand fishing, the proposed method exhibited great potential for screening of bioactive compounds from complex matrices.