Instituto de Neurobiología, Campus UNAM-Juriquilla, Universidad Nacional Autónoma de México (UNAM), México D.F., México.
Curr Med Chem. 2010;17(21):2253-60. doi: 10.2174/092986710791331031.
Ornithine transcarbamylase (OTC; EC 2.1.3.3) is a one-carbon-unit transferring enzyme that synthesizes citrulline using ornithine and carbamoylphosphate as substrates. It is involved in the metabolic transformation of arginine and proline, and it participates in the urea cycle in vertebrates and in the formation of putrescine in plants. Its enzymatic reaction is consistent with a ping-pong mechanism. OTC is expressed in a large variety of organisms from bacteria to mammals. Its gene can be regulated by glucocorticoids and other transcriptional factors such as C/EBP and HNF-4. The functional enzyme exists mostly as a trimer with an approximate molecular weight of 38 kDa. Inborn errors associated with a deficiency of OTC activity cause mainly urea cycle-related disorders, and lead to hyperammonemic states that may become lethal. In humans and experimental animals, OTC is localized in the mitochondrial matrix, mainly in the liver, but it is also in the intestinal epithelial cells. Some states of hepatotoxicity are associated with hepatocyte disruption and release of OTC into the bloodstream. However, recent evidence suggests that during active cell proliferation (e.g., during liver regeneration), OTC is also released from the hepatic tissue but without apparent damage. In this situation, extracellular and circulating hepatic OTC could be playing a different role, possibly functioning as a signaling molecule.
鸟氨酸氨基甲酰转移酶（OTC；EC 2.1.3.3）是一种一碳单位转移酶，它使用鸟氨酸和氨甲酰磷酸作为底物合成瓜氨酸。它参与精氨酸和脯氨酸的代谢转化，并且在脊椎动物中参与尿素循环，在植物中参与腐胺的形成。其酶促反应符合乒乓机制。OTC 在从细菌到哺乳动物的各种生物体中表达。其基因可以被糖皮质激素和其他转录因子（如 C/EBP 和 HNF-4）调节。功能性酶主要以三聚体形式存在，分子量约为 38 kDa。与 OTC 活性缺乏相关的先天性错误主要导致尿素循环相关疾病，并导致可能致命的高氨血症状态。在人和实验动物中，OTC 定位于线粒体基质中，主要在肝脏中，但也存在于肠上皮细胞中。某些肝毒性状态与肝细胞破坏和 OTC 释放到血液中有关。然而，最近的证据表明，在活跃的细胞增殖期间（例如，在肝再生期间），OTC 也从肝组织中释放出来，但没有明显的损伤。在这种情况下，细胞外和循环中的肝 OTC 可能发挥不同的作用，可能作为信号分子发挥作用。
