title: Characterization of carbonic anhydrase XIII in the erythrocytes of the Burmese python, Python molurus bivittatus.
abstract: Carbonic anhydrase (CA) is one of the most abundant proteins found in vertebrate erythrocytes with the majority of species expressing a low activity CA I and high activity CA II. However, several phylogenetic gaps remain in our understanding of the expansion of cytoplasmic CA in vertebrate erythrocytes. In particular, very little is known about isoforms from reptiles. The current study sought to characterize the erythrocyte isoforms from two squamate species, Python molurus and Nerodia rhombifer, which was combined with information from recent genome projects to address this important phylogenetic gap. Obtained sequences grouped closely with CA XIII in phylogenetic analyses. CA II mRNA transcripts were also found in erythrocytes, but found at less than half the levels of CA XIII. Structural analysis suggested similar biochemical activity as the respective mammalian isoforms, with CA XIII being a low activity isoform. Biochemical characterization verified that the majority of CA activity in the erythrocytes was due to a high activity CA II-like isoform; however, titration with copper supported the presence of two CA pools. The CA II-like pool accounted for 90 % of the total activity. To assess potential disparate roles of these isoforms a feeding stress was used to up-regulate CO2 excretion pathways. Significant up-regulation of CA II and the anion exchanger was observed; CA XIII was strongly down-regulated. While these results do not provide insight into the role of CA XIII in the erythrocytes, they do suggest that the presence of two isoforms is not simply a case of physiological redundancy.
authors.affiliation: Department of Marine Science, University of Texas at Austin, Marine Science Institute, 750 Channel View Drive, Port Aransas, TX 78418, USA. Electronic address: a.esbaugh@austin.utexas.edu.
authors.forename: A J
authors.initials: AJ
authors.lastname: Esbaugh
authors.affiliation: Department of Biological Sciences, University of Alabama, Tuscaloosa, AL 35487-0344, USA.
authors.forename: S M
authors.initials: SM
authors.lastname: Secor
authors.affiliation: Division of Marine Biology and Fisheries, University of Miami, Rosenstiel School of Marine and Atmospheric Science, 4600 Rickenbacker Causeway, Miami, FL 33149, USA.
authors.forename: M
authors.initials: M
authors.lastname: Grosell
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport; D017821:Boidae / Q000097:blood* / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D002245:Carbon Dioxide / Q000378:metabolism; D002256:Carbonic Anhydrases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D003593:Cytoplasm / Q000201:enzymology; D004435:Eating; D004912:Erythrocytes / Q000166:cytology / Q000201:enzymology*; D007527:Isoenzymes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D010802:Phylogeny; D017421:Sequence Analysis; D014158:Transcription, Genetic
chemical_list: D007527:Isoenzymes; D002245:Carbon Dioxide; D002256:Carbonic Anhydrases
keywords: CA I; CA XIII; Carbonic anhydrase isoforms; Red blood cells; Specific dynamic action