O'Leary K A, Day A J, Needs P W, Sly W S, O'Brien N M, Williamson G
Nutrition, Health and Consumer Sciences Division, Institute of Food Research, Norwich, UK.
FEBS Lett. 2001 Aug 10;503(1):103-6. doi: 10.1016/s0014-5793(01)02684-9.
Quercetin glucuronides are the main circulating metabolites of quercetin in humans. We hypothesise that the potential availability of the aglycone within tissues depends on the substrate specificity of the deconjugating enzyme beta-glucuronidase towards circulating flavonoid glucuronides. Human tissues (small intestine, liver and neutrophils) exhibited beta-glucuronidase against quercetin glucuronides. The various quercetin glucuronides were deconjugated at similar rates, but liver cell-free extracts were the most efficient and the activity was completely inhibited by saccharo-1,4-lactone (a beta-glucuronidase inhibitor). Furthermore, pure recombinant human beta-glucuronidase hydrolysed various flavonoid glucuronides, with a 20-fold variation in catalytic efficiency (k(cat)/K(m)=1.3x10(3) M(-1) s(-1) for equol-7-O-glucuronide and 26x10(3) M(-1) s(-1) for kaempferol-3-O-glucuronide). Similar catalytic efficiencies were obtained for quercetin O-glucuronides substituted at different positions. These results show that flavonoid glucuronides can be deconjugated by microsomal beta-glucuronidase from various human cells.
槲皮素葡萄糖醛酸苷是槲皮素在人体内的主要循环代谢产物。我们推测，苷元在组织内的潜在可利用性取决于去结合酶β - 葡萄糖醛酸酶对循环类黄酮葡萄糖醛酸苷的底物特异性。人体组织（小肠、肝脏和中性粒细胞）表现出针对槲皮素葡萄糖醛酸苷的β - 葡萄糖醛酸酶活性。各种槲皮素葡萄糖醛酸苷以相似的速率去结合，但肝细胞无细胞提取物效率最高，且该活性被糖 - 1,4 - 内酯（一种β - 葡萄糖醛酸酶抑制剂）完全抑制。此外，纯重组人β - 葡萄糖醛酸酶可水解各种类黄酮葡萄糖醛酸苷，催化效率有20倍的差异（对雌马酚 - 7 - O - 葡萄糖醛酸苷而言，k(cat)/K(m)=1.3×10³ M⁻¹ s⁻¹；对山奈酚 - 3 - O - 葡萄糖醛酸苷而言，k(cat)/K(m)=26×10³ M⁻¹ s⁻¹）。不同位置被取代的槲皮素O - 葡萄糖醛酸苷也获得了相似的催化效率。这些结果表明，类黄酮葡萄糖醛酸苷可被来自各种人体细胞的微粒体β - 葡萄糖醛酸酶去结合。
