Enzymatic synthesis of 4-hydroxyphenyl beta-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 beta-D-oligoxylosides, beta-(Xyl)(n)-HQ (n=1-4), by one step reaction. The obtained beta-(Xyl)(n)-HQ inhibited mushroom tyrosinase, which catalyzes the oxidation of L-DOPA to L-DOPA quinine, and the IC(50) values of beta-Xyl-HQ, beta-(Xyl)(2)-HQ, beta-(Xyl)(3)-HQ, and beta-(Xyl)(4)-HQ were 3.0, 0.74, 0.48, and 0.18 mM respectively. beta-(Xyl)(4)-HQ showed 35-fold more potent inhibitory activity than beta-arbutin (4-hydroxyphenyl beta-D-glucopyranoside), of which the IC(50) value was measured to be 6.3 mM. Kinetic analysis revealed that beta-(Xyl)(2)-HQ, beta-(Xyl)(3)-HQ, and beta-(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.