Enzymatic Synthesis of 4-Hydroxyphenyl β-D-Oligoxylosides and Their Notable Tyrosinase Inhibitory Activity

We have purified and characterized an oligoxylosyl transfer enzyme (OxtA) from Bacillus sp. strain KT12. In the present study, a N-terminally His-tagged recombinant form of the enzyme, OxtA(H)E, was overproduced in Escherichia coli and applied to the reaction with xylan and hydroquinone to produce 4-hydroxyphenyl β-D-oligoxylosides, β-(Xyl)n-HQ (n=1–4), by one step reaction. The obtained β-(Xyl)n-HQ inhibited mushroom tyrosinase, which catalyzes the oxidation of L-DOPA to L-DOPA quinine, and the IC50 values of β-Xyl-HQ, β-(Xyl)2-HQ, β-(Xyl)3-HQ, and β-(Xyl)4-HQ were 3.0, 0.74, 0.48, and 0.18 mM respectively. β-(Xyl)4-HQ showed 35-fold more potent inhibitory activity than β-arbutin (4-hydroxyphenyl β-D-glucopyranoside), of which the IC50 value was measured to be 6.3 mM. Kinetic analysis revealed that β-(Xyl)2-HQ, β-(Xyl)3-HQ, and β-(Xyl)4-HQ competitively inhibited the enzyme, and the corresponding K i values were calculated to be 0.20, 0.29, and 0.057 mM respectively.