Elmamlouk T H, Mukhtar H, Bend J R
J Pharmacol Exp Ther. 1981 Oct;219(1):27-34.
The formation of p-nitrophenylglucuronide from p-nitrophenol and [14C]uridine disphosphoglucuronic acid was demonstrated in intact rat liver nuclei and nuclear membranes. Most of the enzymatic activity in nuclei (80%) was localized in the nuclear envelope. Several in vitro activators of microsomal glucuronyltransferase had no effect on enzyme activity in whole nuclei, but were effective in stimulating the activity in nuclear membranes; however, the magnitude of activation (45%) was much less than with microsomes (500%). UDP-N-acetylglucosamine had no effect on nuclear UDP-glucuronyltransferase activity in whole nuclei or in nuclear membrane preparations. The nuclear membrane enzyme(s) did not obey simple Michaelis-Menten kinetics in native or detergent-activated enzyme preparations. The kinetic behavior did not change upon activation and the apparent Km values remained constant, 1.0 and 0.7 mM for UDP-glucuronic acid and nitrophenol, respectively. Nuclear membrane UDP-glucuronyltransferase activity was increased 3-fold by pretreatment with 3-methylcholanthrene. Phenobarbital or trans-stilbene oxide pretreatment had no effect on nuclear enzyme activity. In contrast, microsomal UDP-glucuronyltransferase activity was increased upon pretreatment with all of these inducers. The results suggest that rat hepatic nuclear glycuronyltransferase activity is localized in the nuclear envelope and that the activity is possibly under a different control mechanism than tha for the microsomes. The properties and physiological significance of the nuclear enzyme are discussed.
在完整的大鼠肝细胞核和核膜中，已证实对硝基苯酚与[14C]尿苷二磷酸葡糖醛酸可形成对硝基苯基葡糖醛酸。细胞核中大部分酶活性（80%）定位于核膜。几种微粒体葡糖醛酸转移酶的体外激活剂对完整细胞核中的酶活性无影响，但能有效刺激核膜中的活性；然而，激活程度（45%）远低于微粒体（500%）。UDP-N-乙酰葡糖胺对完整细胞核或核膜制剂中的核UDP-葡糖醛酸转移酶活性无影响。在天然或去污剂激活的酶制剂中，核膜酶不遵循简单的米氏动力学。激活后动力学行为不变，UDP-葡糖醛酸和对硝基苯酚的表观Km值分别保持恒定，为1.0和0.7 mM。用3-甲基胆蒽预处理可使核膜UDP-葡糖醛酸转移酶活性增加3倍。苯巴比妥或反式氧化茋预处理对核酶活性无影响。相比之下，用所有这些诱导剂预处理后，微粒体UDP-葡糖醛酸转移酶活性增加。结果表明，大鼠肝细胞核葡糖醛酸转移酶活性定位于核膜，且该活性可能受与微粒体不同的控制机制调控。文中讨论了核酶的性质和生理意义。
