Ho K J, Ho L H, Kruger O R
J Lab Clin Med. 1979 Jun;93(6):916-25.
beta-Glucuronidase activity determined in 100 diluted bile samples from 12 rats with bile duct fistula by using phenolphthalein glucuronide as substrate incubated at 56 degrees C and pH 6 was 636 +/- 650 (mean +/- S.D.) modified Sigma units/ml. The enzyme had an optimal pH of 6.0 and was inhibited slightly by cholate by markedly by chenodeoxycholate and deoxycholate. The biliary beta-glucuronidase had, thus, low activity under normal physiologic condition because of the high pH (8.1) and high bile salt content (20 mumoles/ml) of the bile. The enzyme kinetic studies revealed that the direct bilirubin was a competitive inhibitor to phonolphthalein glucuronide for the enzyme. The affinity of the former to the enzyme was 163 times that of the latter. The studies provided a method for measuring the true activity of biliary beta-glucuronidase (Vmax) devoid of interfering factors by measuring the enzyme velocity (v) in the diluted bile with at least five different concentrations of substrate (s). The plotting of (1/v) vs. (1/s) should yield the y intercept or (1/Vmax).
以酚酞葡糖苷酸为底物，在56℃和pH 6条件下孵育，对12只胆管瘘大鼠的100份稀释胆汁样本进行β - 葡糖醛酸酶活性测定，结果为636±650（平均值±标准差）改良西格玛单位/毫升。该酶的最适pH为6.0，胆酸盐对其有轻微抑制作用，鹅去氧胆酸盐和脱氧胆酸盐则有明显抑制作用。因此，由于胆汁的高pH值（8.1）和高胆汁盐含量（20微摩尔/毫升），在正常生理条件下胆汁β - 葡糖醛酸酶活性较低。酶动力学研究表明，直接胆红素是该酶对酚酞葡糖苷酸的竞争性抑制剂。前者对酶的亲和力是后者的163倍。这些研究提供了一种通过用至少五种不同浓度的底物（s）测量稀释胆汁中的酶速度（v）来测量无干扰因素的胆汁β - 葡糖醛酸酶真实活性（Vmax）的方法。绘制（1/v）对（1/s）的图应得到y轴截距或（1/Vmax）。
