Enzymatic transformation of curcumin-glucuronide. Curcumin-glucuronide (40 μM) was reacted with (A) lactoperoxidase (LPO), (B) myeloperoxidase (MPO), (C) tyrosinase, and (D) xanthine oxidase, each in the presence (A, B) or absence (C, D) of H2O2 (20 μM). Samples were scanned following the addition of enzyme and H2O2 in 2-min intervals for the next 20 min. In (E) and (F) the samples from myeloperoxidase- and lactoperoxidase-catalyzed transformation of curcumin-glucuronide were analyzed using LC-MS in the positive ion mode. Ion traces for curcumin-glucuronide (m/z 545; upper) and bicyclopentadione-glucuronide (BCP-Gluc.; m/z 577; lower) are shown.