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 CO2 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 CO2 concentrations decreases when the external NH4+ concentration decreases, to the point of being undetectable when NH4+ supply restricts the rate of photoautotrophic growth. The expression of mtCA can also be induced at supra-atmospheric partial pressure of CO2 by increasing the NH4+ concentration in the growth medium. Conditions that favor mtCA expression usually also stimulate anaplerosis. We therefore propose that the mtCA is involved in supplying HCO3- for anaplerotic assimilation catalyzed by phosphoenolpyruvate carboxylase, which provides C skeletons for N assimilation under some circumstances.

An anaplerotic role for Mitochondrial Carbonic Anhydrase in Chlamydomonas reinhardti / Giordano, Mario; Norici, Alessandra; Forssen, M.; Eriksson, M; Raven, Ja. - In: PLANT PHYSIOLOGY. - ISSN 0032-0889. - STAMPA. - 132:(2003), pp. 2126-2134.

An anaplerotic role for Mitochondrial Carbonic Anhydrase in Chlamydomonas reinhardti

GIORDANO, Mario;NORICI, ALESSANDRA;
2003-01-01

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 CO2 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 CO2 concentrations decreases when the external NH4+ concentration decreases, to the point of being undetectable when NH4+ supply restricts the rate of photoautotrophic growth. The expression of mtCA can also be induced at supra-atmospheric partial pressure of CO2 by increasing the NH4+ concentration in the growth medium. Conditions that favor mtCA expression usually also stimulate anaplerosis. We therefore propose that the mtCA is involved in supplying HCO3- for anaplerotic assimilation catalyzed by phosphoenolpyruvate carboxylase, which provides C skeletons for N assimilation under some circumstances.
2003
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11566/29401
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