An anaplerotic role for mitochondrial carbonic anhydrase in Chlamydomonas reinhardtii.
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.
Giordano
Mario
M
Dipartimento di Scienze del Mare, Università Politecnica delle Marche, Via Brecce Bianche, 60131 Ancona, Italy. giordano@unian.it
Norici
Alessandra
A
Forssen
Magnus
M
Eriksson
Mats
M
Raven
John A
JA
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
D001639:Bicarbonates; D000644:Quaternary Ammonium Compounds; D002245:Carbon Dioxide; D002244:Carbon; D002256:Carbonic Anhydrases; D009584:Nitrogen