title: An anaplerotic role for mitochondrial carbonic anhydrase in Chlamydomonas reinhardtii.
abstract: Previous studies of the mitochondrial carbonic anhydrase (mtCA) of Chlamydomonas reinhardtii showed that expression of the two genes encoding this enzyme activity required photosynthetically active radiation and a low CO(2) concentration. These studies suggested that the mtCA was involved in the inorganic carbon-concentrating mechanism. We have now shown that the expression of the mtCA at low CO(2) concentrations decreases when the external NH(4)(+) concentration decreases, to the point of being undetectable when NH(4)(+) supply restricts the rate of photoautotrophic growth. The expression of mtCA can also be induced at supra-atmospheric partial pressure of CO(2) by increasing the NH(4)(+) concentration in the growth medium. Conditions that favor mtCA expression usually also stimulate anaplerosis. We therefore propose that the mtCA is involved in supplying HCO(3)(-) for anaplerotic assimilation catalyzed by phosphoenolpyruvate carboxylase, which provides C skeletons for N assimilation under some circumstances.
authors.affiliation: Dipartimento di Scienze del Mare, Università Politecnica delle Marche, Via Brecce Bianche, 60131 Ancona, Italy. giordano@unian.it
authors.forename: Mario
authors.initials: M
authors.lastname: Giordano
authors.forename: Alessandra
authors.initials: A
authors.lastname: Norici
authors.forename: Magnus
authors.initials: M
authors.lastname: Forssen
authors.forename: Mats
authors.initials: M
authors.lastname: Eriksson
authors.forename: John A
authors.initials: JA
authors.lastname: Raven
mesh_terms: D000818:Animals; D001639:Bicarbonates / Q000378:metabolism; D002244:Carbon / Q000378:metabolism; D002245:Carbon Dioxide / Q000494:pharmacology; D002256:Carbonic Anhydrases / Q000378:metabolism*; D016825:Chlamydomonas reinhardtii / Q000187:drug effects / Q000201:enzymology*; D005786:Gene Expression Regulation / Q000187:drug effects; D008928:Mitochondria / Q000201:enzymology*; D009584:Nitrogen / Q000378:metabolism; D010788:Photosynthesis; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology
chemical_list: D001639:Bicarbonates; D000644:Quaternary Ammonium Compounds; D002245:Carbon Dioxide; D002244:Carbon; D002256:Carbonic Anhydrases; D009584:Nitrogen