Effects of Ca2+, Zn2+ and Cd2+ on uridine diphosphate-glucuronyltransferase and .BETA.-glucuronidase activities in rat liver microsomes.
作者:Masayoshi YAMAGUCHI、Seiichi MORI、Yasunobu SUKETA
DOI:10.1248/cpb.38.159
日期:——
The effect of various metals on uridine diphosphate (UDP)-glucuronyltransferase and β-glucuronidase activities in rat liver microsomes was investigated. The presence of Mn2+, Cd2+, Zn2+, V5+, Ni2+, Co2+, Cu+ or Ca2+ (20μM) in the enzyme reaction mixture did not a significant alteration of UDP-glucuronyltransferase activity in hepatic microsomes. Of these metals, Zn2+ and Cd2+ (20μM) caused a remarkable increase in hepatic microsomal β-glucuronidase activity. Appreciable effects of Zn2+ and Cd2+ on β-glucuronidase activity were seen at 5.0 μM, and the effects were saturated at 50 μM. Ca2+ (5.0-50 μM) and/or the Ca2+-binding protein regucalcin (2.0μM) did not have an appreciable effect on UDP-glucuronyltransferase and β-glucuronidase activities in hepatic microsomes. Thus, Zn2+ and Cd2+ uniquely increased β-glucuronidase activity. The Zn2+-and Cd2+-induced increase in β-glucuronidase activity was completely reversed by the presence of an SH group-protecting reagent (dithiothreitl). The response of the microsomal enzyme to Zn2+ and Cd2+ (20 μM) was no longer seen after treatment with 0.2% Triton X-100 [polyoxyethylene(10) octylphenyl ether], indicating that the stimulation by these metals is dependent on membrane association. The present study suggests that, of various metals tested, Zn2+ and Cd2+ can uniquely increase hepatic microsomal β-glucuronidase actibity, and that their effect is based on binding to membranous SH groups, beside the enzyme protein.
研究了各种金属对大鼠肝脏微粒体中二磷酸尿苷(UDP)-葡糖醛酸转移酶和β-葡糖醛酸酶活性的影响。在酶反应混合物中加入 Mn2+、Cd2+、Zn2+、V5+、Ni2+、Co2+、Cu+ 或 Ca2+(20μM)不会显著改变肝微粒体中 UDP-葡糖醛酸基转移酶的活性。在这些金属中,Zn2+ 和 Cd2+(20μM)能显著提高肝微粒体 β-葡萄糖醛酸酶的活性。Zn2+ 和 Cd2+ 在 5.0 μM 时对β-葡糖醛酸酶活性有明显影响,在 50 μM 时影响达到饱和。Ca2+ (5.0-50 μM)和/或 Ca2+ 结合蛋白雷公藤苷元(2.0 μM)对肝微粒体中的 UDP-葡萄糖醛酸转移酶和 β-葡萄糖醛酸酶活性没有明显影响。因此,Zn2+ 和 Cd2+ 能独特地提高 β-葡糖醛酸酶的活性。Zn2+ 和 Cd2+ 诱导的 β-葡糖醛酸酶活性的增加在存在 SH 基团保护试剂(二硫代苏氨酸)的情况下被完全逆转。经 0.2% Triton X-100 [聚氧乙烯(10)辛基苯基醚]处理后,微粒体酶对 Zn2+ 和 Cd2+ (20 μM)的反应不再出现,这表明这些金属的刺激作用依赖于膜结合。本研究表明,在测试的各种金属中,Zn2+ 和 Cd2+ 能独特地提高肝微粒体 β-葡萄糖醛酸酶的活性,它们的作用是基于与膜上的 SH 基团结合,而不是酶蛋白。