Biochemical Adaptation Laboratory, Department of Zoology, Banaras Hindu University, Varanasi 221005, India.
Biochem Biophys Res Commun. 2010 Jan 1;391(1):1-5. doi: 10.1016/j.bbrc.2009.11.018. Epub 2009 Nov 11.
Arginase catalyses the last step of the urea cycle. At least two isoenzymes of arginase are known; cytosolic ARG I and mitochondrial ARG II. ARG I is predominantly expressed in liver cytosol, as a part of urea cycle in ureotelic animals. The second isoform ARG II is primarily responsible for non-ureogenic functions, expressed in mitochondria of both hepatic and non-hepatic tissues in most vertebrates. Most micro-organisms and invertebrates are known to have only one type of arginase, whose function is unrelated to ornithine-urea cycle (OUC). However, in ureo-osmotic marine elasmobranchs arginase is localized in liver mitochondria as a part of OUC to synthesize urea for osmoregulation. An evolutionary transition occurred in arginase enzyme in terrestrial ureotelic vertebrates, with the evolution of ARG I from a pre-existing ancestral mitochondrial ARG II. This cytosolic ARG I activity is supposed to have first appeared in lung fishes, but the 40% and 60% distribution of arginase I and II activity in liver and kidney tissue of Heteropneustes fossilis indicates reconsideration of the above fact.
精氨酸酶催化尿素循环的最后一步。目前已知至少有两种精氨酸酶同工酶：胞质 ARG I 和线粒体 ARG II。ARG I 主要在肝脏细胞质中表达，作为尿生物合成动物尿素循环的一部分。第二种同工酶 ARG II 主要负责非尿生物合成功能，在大多数脊椎动物的肝和非肝组织的线粒体中表达。大多数微生物和无脊椎动物都只有一种类型的精氨酸酶，其功能与鸟氨酸-尿素循环（OUC）无关。然而，在尿渗海洋软骨鱼类中，精氨酸酶定位于肝脏线粒体中，作为 OUC 的一部分，用于合成尿素以进行渗透调节。在陆地尿生物合成脊椎动物中，精氨酸酶酶发生了进化转变，ARG I 从先前存在的线粒体 ARG II 进化而来。这种胞质 ARG I 活性似乎首先出现在肺鱼中，但在异鲷的肝脏和肾脏组织中，ARG I 和 II 活性的 40%和 60%分布表明需要重新考虑上述事实。
