Ho K J, Ho L H
Enzyme. 1980;25(6):361-70.
beta-Glucuronidase activity was determined in dialyzed and undialyzed urine from 50 healthy adult males by single-point and enzyme kinetic measuring systems. The enzyme had a pH optimum of 5.2 and a Michaelis constant of 1.465 +/- 0.206 mmol/l (mean +/- SD) of phenolphthalein glucuronide. Substrate inhibition occurred at a concentration of 0.006 mol/l in one fourth of the urine samples. A significant amount of a competitive inhibitor, D-glucaro-1,4-lactone, was present in one third of the specimens. The activity measured by the single-point determination was always lower than the maximal velocity, particularly in the presence of the competitive inhibitor and substrate inhibition. Such pitfalls could be avoided by the enzyme kinetic method which not only permits the detection of substrate inhibition of the enzyme and the elimination of 2-hour dialysis of urine, but also allows the determination of both the maximal velocity of the enzyme and the quantity of D-glucaro-1,4-lactone in urine.
采用单点测定法和酶动力学测定系统，对50名健康成年男性的透析尿液和未透析尿液中的β-葡萄糖醛酸酶活性进行了测定。该酶的最适pH为5.2，对酚酞葡萄糖醛酸苷的米氏常数为1.465±0.206 mmol/L（平均值±标准差）。四分之一的尿液样本在浓度为0.006 mol/L时出现底物抑制。三分之一的样本中存在大量竞争性抑制剂D-葡萄糖酸-1,4-内酯。单点测定法测得的活性总是低于最大速度，尤其是在存在竞争性抑制剂和底物抑制的情况下。酶动力学方法可以避免这些陷阱，该方法不仅可以检测酶的底物抑制作用，无需对尿液进行2小时透析，还可以测定酶的最大速度和尿液中D-葡萄糖酸-1,4-内酯的含量。
