Green M D, Tephly T R
Department of Pharmacology, University of Iowa 52242, USA.
Drug Metab Dispos. 1996 Mar;24(3):356-63.
Glucuronide conjugation of tertiary amine xenobiotics represents a unique and important metabolic pathway for these compounds in humans. In this study, we show that human UDP-glucuronosyltransferase 1.4 protein, stably expressed in human embryonic kidney 293 cells, catalyzes the N-glucuronidation of primary, secondary, and tertiary amine substrates. In addition, the substrate specificity of the expressed enzyme toward many hydroxylated and carboxylic acid-containing compounds was examined. Of the hydroxylated compounds tested, only sapogenins gave glucuronidation rates comparable with those observed for amine substrates. The apparent KM and Vmax values for sapogenins were such that the efficiency of glucuronidation (Vmax/KM) for these compounds was higher than that determined for amine substrates. Human UDP-glucuronosyltranferase 1.4 also catalyzes the glucuronidation of monoterpenoid alcohols and simple phenolic compounds. The enzyme kinetic values determined for these substrates suggested that this enzyme may have relatively limited significance for the conjugation of these classes of compounds. Of the endobiotics tested, androstanediol and progestins were glucuronidated at high rates by expressed human UDP-glucuronosyltransferase 1.4 protein. The glucuronidation efficiency for 5alpha-pregnane-3beta,20alpha-diol was comparable with that determined for the sapogenins. Because UDP-glucuronosyltransferases are integral membrane proteins, the effects of different detergents on the catalytic activity of the expressed enzyme were determined. The results show that detergents (such as Lubrol PX, Emulgen 911, and Triton X-100) are inhibitory for the quaternary ammonium-linked glucuronidation of chlorpromazine and imipramine catalyzed by expressed human UDP-glucuronosyltransferase 1.4. In contrast, CHAPS and nonanoyl-N-methylglucamide are less inhibitory toward the glucuronidation of these compounds. The results suggest that human UDP-glucuronosyltransferase 1.4 may be an important enzyme for the detoxication of environmentally derived amines and sapogenins and for the conjugation of progestins.
叔胺类外源性物质的葡萄糖醛酸结合反应是这些化合物在人体内独特且重要的代谢途径。在本研究中，我们发现稳定表达于人类胚胎肾293细胞中的人尿苷二磷酸葡萄糖醛酸基转移酶1.4蛋白催化伯胺、仲胺和叔胺底物的N - 葡萄糖醛酸化反应。此外，还检测了所表达酶对许多含羟基和羧酸化合物的底物特异性。在所测试的羟基化化合物中，只有皂草苷的葡萄糖醛酸化速率与胺底物的相当。皂草苷的表观米氏常数（KM）和最大反应速度（Vmax）值表明，这些化合物的葡萄糖醛酸化效率（Vmax/KM）高于胺底物。人尿苷二磷酸葡萄糖醛酸基转移酶1.4也催化单萜醇和简单酚类化合物的葡萄糖醛酸化反应。针对这些底物测定的酶动力学值表明，该酶对这些类化合物的结合反应可能意义相对有限。在所测试的内源性物质中，雄甾二醇和孕激素被所表达的人尿苷二磷酸葡萄糖醛酸基转移酶1.4蛋白高效葡萄糖醛酸化。5α - 孕烷 - 3β,20α - 二醇的葡萄糖醛酸化效率与皂草苷相当。由于尿苷二磷酸葡萄糖醛酸基转移酶是整合膜蛋白，因此测定了不同去污剂对所表达酶催化活性的影响。结果表明，去污剂（如Lubrol PX、Emulgen 911和Triton X - 100）对所表达的人尿苷二磷酸葡萄糖醛酸基转移酶1.4催化的氯丙嗪和丙咪嗪的季铵连接葡萄糖醛酸化反应具有抑制作用。相比之下，CHAPS和壬酰 - N - 甲基葡糖酰胺对这些化合物的葡萄糖醛酸化反应抑制作用较小。结果表明，人尿苷二磷酸葡萄糖醛酸基转移酶1.4可能是环境来源胺类和皂草苷解毒以及孕激素结合反应的重要酶。
