Metabolic Compartmentation of Vertebrate Glutamine Synthetase

本项目的总体目标是阐明 可能的分子事件导致了 谷氨酰胺合成酶在肝组织中的区室化 脊椎动物进化 这种酶的定位使得 对于发展尿酸作为一种主要的排泄 氮代谢 大多数线粒体蛋白质编码为 在细胞核中，在细胞质中翻译，并靶向 线粒体的N-末端信号序列。 的较大尺寸 前酶允许其与成熟酶区分开， 酵素 我们已经证明，这可能是真正的板鳃类 肝脏线粒体谷氨酰胺合成酶，我们现在打算 表征板鳃亚纲动物肝脏前酶的输入 在体内和体外的线粒体。 我们还发现，在 鸟类和短吻鳄之间没有明显的大小差异 在新生和成熟谷氨酰胺合成酶肽之间， 肝脏，尽管其线粒体基质定位在组织中。 为了确定是否有内部靶向序列 在禽类酶中，我们将克隆和测序谷氨酰胺， 合成酶mRNA cDNA。 酶 仍然存在于后者组织的胞质溶胶中， 两者的推导的氨基酸序列应该给出一些 关于所用信号序列的性质和位置的线索 输入肝酶 我们还将获得推导的 板鳃类和可能的龟前谷氨酰胺的序列 合成酶用于比较目的。 这个比较应该给 可能发生的变化的一些迹象， 从一个经典的前序机制， 酶靶向肝线粒体在原始 脊椎动物的任何机制，用于高等排尿酸 脊椎动物 这项关于酶是如何在细胞内 靶向特定的细胞区室对细胞 生物学和生物化学。 酶活性的调节是 了解新陈代谢的关键问题。//

The overall goal of this project is an elucidation of the possible molecular events that led to the mitchondrial compartmentation of glutamine synthetase in liver tissue during vertebrate evolution. This localization of the enzyme allowed for the development of uricoteley as a major kind of excretory nitrogen metabolism. Most mitochondrial proteins are coded for in the nucleus, translated in cytosol, and targeted to mitochondria by N-terminal signal sequences. The larger size of the pre-enzyme allows it to be distinguished from the mature enzyme. We have shown this to probably be true for elasmobranch liver mitochondrial glutamine synthetase and we now intend to characterize the import of the pre-enzyme by elasmobranch liver mitochondria in vivo and in vitro. We have also found that in birds and alligators there is no detectable size difference between the nascent and mature glutamine synthetase peptide in liver, despite its mitochondrial matrix localization in tissue. In order to determine if there is an internal targeting sequence in the avian enzyme, we will clone and sequence glutamine synthetase mRNA cDNA from both liver and brain. The enzyme remains in the cytosol in the latter tissue so a comparison of the deduced amino acid sequences for the two should give some clue as to the nature and location of the signal sequence used for import of the liver enzyme. We also will obtain the deduced sequences for elasmobranch and possibly tortoise pre-glutamine synthetase for comparative purposes. This comparison should give some indication of the possible changes that have occured during evolution that led from a classical presequence mechanism for targeting of the enzyme to liver mitochondria in primitive vertebrates to whatever the mechanism used in higher uricotelic vertebrates. This research on the molecular mechanisms of how enzymes are targeted to specific cell compartments is significant to cell biology and biochemistry. The regulation of enzyme activity is a key question for understanding metabolism.//