Physiological roles of a new copper-binding protein : relationship between new copper-binding protein and hereditary copper

铜是一种必需的微量元素，需要在必要的浓度和毒性之间进行微妙的细胞平衡。金属硫蛋白(MT)是一种低相对分子质量的重结合蛋白，在铜的动态平衡和解毒中起着重要作用。本研究采用一种新的铜结合蛋白和铜结合蛋白的新纯化方法，在有氧条件下对单次或多次铜注射诱导的大鼠铜结合蛋白进行了鉴定，确定为铜结合蛋白和/或一种新的铜结合蛋白。我们证明了一种新的铜诱导蛋白的存在，这种蛋白不属于MT基团，因为该蛋白是一种低半胱氨酸含量的蛋白，每个分子结合了两个铜原子，从而解决了这一困惑。结果表明，在大鼠肝脏中，单次注射铜只诱导出铜-MT，而多次注射铜则同时出现了铜-MT和新蛋白。这一结果表明，当肝脏铜含量增加并达到一定的阈值时，过量的铜合成了新的蛋白质，而铜-MT没有充分解毒，以服务于铜的解毒。此外，我们还建立了门克氏病(X-连锁铜代谢紊乱)模型小鼠肾脏中过量的铜，发现为铜-MT。大脑皮层近曲小管细胞中以铜-MT为主。在大脑皮层也观察到MT mRNA，表明该蛋白在该区域被生物合成。另一方面，新的铜结合蛋白在黄斑小鼠的肾脏中几乎没有检测到。从这些结果来看，新的蛋白质被认为在铜代谢中起关键作用。

Cu is an essential trace element which requires a delicate cellular balance between a necessary concentration and toxicity. Metallothionein (MT), a low molecular weight heavy-binding protein, plays an important role in Cu homeostasis and detoxification. In this study, the Cu-binding low molecular weight proteins induced by single or multiple Cu-injection rats were identified as Cu-MTs and/or a new Cu-binding protein using a new purification procedure of both of the new protein and Cu-MT under the aerobic condition.There were many debate on the existence of MT and other Cu-binding proteins which appeared in tissues of Cu-loaded animals. We settled the confusion by demonstrating of the presence of a new Cu-induced protein which did not belong to MT group, because the protein was a low cystein content and bound two Cu atoms per a molecule. We did show that only Cu-MT was induced by a single injection of Cu in rat liver and both of Cu-MT and the new protein appeared by the multiple injections of Cu. This result suggests that new protein was synthesized by excessive Cu which was not sufficiently detoxified by Cu-MT to serve detoxification of Cu when the hepatic Cu content increased and reached a certain threshold value.In addition, we established that excess amounts of Cu in the kidney of Macular mice, a model for Menke's disease (X-linked disorder of Cu metabolism), were found as Cu-MT. The Cu-MT was predominant in the proximal convoluted tubule cells of the cortex. MT mRNA was also observed in the cortex, indicating that the protein was biosynthesized in this region. On the other hand, the new Cu-binding protein was hardly detected in the kidney of macular mice. From these results the new protein was considered to play a key role in Cu-metabolism.