title: Does fish represent an intermediate stage in the evolution of ureotelic cytosolic arginase I?
abstract: 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.
authors.affiliation: Biochemical Adaptation Laboratory, Department of Zoology, Banaras Hindu University, Varanasi 221005, India. shilp.vastava@gmail.com
authors.forename: Shilpee
authors.initials: S
authors.lastname: Srivastava
authors.forename: B K
authors.initials: BK
authors.lastname: Ratha
mesh_terms: D000818:Animals; D001119:Arginase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D003600:Cytosol / Q000201:enzymology*; D019143:Evolution, Molecular; D005399:Fishes / Q000254:growth & development* / Q000378:metabolism; D007527:Isoenzymes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D007668:Kidney / Q000201:enzymology; D008099:Liver / Q000201:enzymology; D008930:Mitochondria, Liver / Q000201:enzymology; D014018:Tissue Distribution; D014508:Urea / Q000378:metabolism*
chemical_list: D007527:Isoenzymes; D014508:Urea; D001119:Arginase