Thomassin J, Boutin J A, Siest G
Pharmacol Res Commun. 1985 Nov;17(11):1005-15. doi: 10.1016/0031-6989(85)90107-9.
We studied the in vitro capability of hepatic microsomal UDP-glucuronosyltransferase (UDPGT) in male rats to conjugate 22 natural xenobiotics which are known to be excreted as glucuronides in vivo. We clearly demonstrated that the Vmax can range in a decreasing scale for the following families of aglycones: 7-hydroxylated coumarins greater than 2-naphthol and phenols greater than monoterpenoid alcohols greater than 4-hydroxylated coumarins. The Km app. cannot be arranged in the same scale. This suggests that the catalytic mechanism of UDPGT is dependent on the hydroxyl group reactivity rather than on the binding interaction at the active site expressed by the Km app. The effects of various concentrations of detergent (Triton X-100) were determined on specificity (apparent Km) and activity (Vmax). For the 22 aglycones we showed that activation caused a variation in the Vmax which was a function of the concentration in detergent. The maximum of this activation did not always correspond to the same detergent/protein weight ratio. The impact of activation on Km app. was less clear since the variations observed were slightly different.
我们研究了雄性大鼠肝微粒体UDP-葡萄糖醛酸基转移酶（UDPGT）在体外结合22种天然外源性物质的能力，这些外源性物质在体内已知是以葡萄糖醛酸苷形式排泄的。我们清楚地证明，对于以下苷元家族，Vmax可以按递减顺序排列：7-羟基香豆素大于2-萘酚，酚类大于单萜醇类大于4-羟基香豆素。Km app. 不能按相同顺序排列。这表明UDPGT的催化机制取决于羟基的反应性，而不是取决于由Km app. 表示的活性位点处的结合相互作用。测定了不同浓度去污剂（Triton X-100）对特异性（表观Km）和活性（Vmax）的影响。对于这22种苷元，我们表明激活导致Vmax发生变化，这是去污剂浓度的函数。这种激活的最大值并不总是对应相同的去污剂/蛋白质重量比。激活对Km app. 的影响不太明显，因为观察到的变化略有不同。
