Department of Epidemiology, NUTRIM School for Nutrition, Toxicology & Metabolism, Maastricht University, The Netherlands.
Drug Metab Pharmacokinet. 2010;25(4):379-87. doi: 10.2133/dmpk.dmpk-10-rg-002.
Flavonoids are inactivated by phase II metabolism and occur in the body as glucuronides. Mammalian beta-glucuronidase released from neutrophils at inflammatory sites may be able to deconjugate and thus activate flavonoid glucuronides. We have studied deconjugation kinetics and pH optimum for four sources of beta-glucuronidase (human neutrophil, human recombinant, myeloid PLB-985 cells, Helix pomatia) with five flavonoid glucuronides (quercetin-3-glucuronide, quercetin-3'-glucuronide, quercetin-4'-glucuronide, quercetin-7-glucuronide, 3'-methylquercetin-3-glucuronide), 4-methylumbelliferyl-beta-D-glucuronide, and para-nitrophenol-glucuronide. All substrate-enzyme combinations tested exhibited first order kinetics. The optimum pH for hydrolysis was between 3.5-5, with appreciable hydrolysis activities up to pH 5.5. At pH 4, the K(m) ranged 44-fold from 22 microM for quercetin-4'-glucuronide with Helix pomatia beta-glucuronidase, to 981 microM for para-nitrophenol-glucuronide with recombinant beta-glucuronidase. V(max) (range: 0.735-24.012 micromol x min(-1) x unit(-1) [1 unit is defined as the release of 1 microM 4-methylumbelliferyl-beta-D-glucuronide per min]) and the reaction rate constants at low substrate concentrations (k) (range: 0.002-0.062 min(-1) x (unit/L)(-1) were similar for all substrates-enzyme combinations tested. In conclusion, we show that beta-glucuronidase from four different sources, including human neutrophils, is able to deconjugate flavonoid glucuronides and non-flavonoid substrates at fairly similar kinetic rates. At inflammatory sites in vivo the pH, neutrophil and flavonoid glucuronide concentrations seem favorable for deconjugation. However, it remains to be confirmed whether this is actually the case.
类黄酮通过 II 相代谢失活，并以葡萄糖醛酸苷的形式存在于体内。在炎症部位从中性粒细胞释放的哺乳动物β-葡糖苷酸酶可能能够去共轭，从而激活类黄酮葡萄糖醛酸苷。我们已经研究了四种来源的β-葡糖苷酸酶（人中性粒细胞、人重组、髓样 PLB-985 细胞、海蜗牛）与五种类黄酮葡萄糖醛酸苷（槲皮素-3-葡萄糖醛酸苷、槲皮素-3'-葡萄糖醛酸苷、槲皮素-4'-葡萄糖醛酸苷、槲皮素-7-葡萄糖醛酸苷、3'-甲基槲皮素-3-葡萄糖醛酸苷）、4-甲基伞形酮-β-D-葡糖苷酸和对硝基苯酚-β-D-葡糖苷酸的去共轭动力学和 pH 最适值。所有测试的底物-酶组合均表现出一级动力学。水解的最佳 pH 值在 3.5-5 之间，在 pH 5.5 时仍具有明显的水解活性。在 pH 4 时，对于海蜗牛β-葡糖苷酸酶的槲皮素-4'-葡萄糖醛酸苷，Km 值范围为 44 倍，为 22 μM，对于重组β-葡糖苷酸酶的对硝基苯酚-β-D-葡糖苷酸，Km 值为 981 μM。Vmax（范围：0.735-24.012 μmol x min-1 x unit-1 [1 个单位定义为每分钟释放 1 μM 4-甲基伞形酮-β-D-葡糖苷酸]）和低底物浓度下的反应速率常数（k）（范围：0.002-0.062 min-1 x （单位/L）-1）对于所有测试的底物-酶组合都相似。总之，我们表明，四种不同来源的β-葡糖苷酸酶，包括人中性粒细胞，能够以相当相似的动力学速率去共轭类黄酮葡萄糖醛酸苷和非类黄酮底物。在体内炎症部位，pH 值、中性粒细胞和类黄酮葡萄糖醛酸苷浓度似乎有利于去共轭。然而，仍有待证实这是否属实。
