Inorganic Carbon Transport and Fixation in Cells of Anabaena variabilis Adapted to Mixotrophic Conditions |
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Authors: | Nieva, Mar Valiente, Eduardo Fernandez |
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Affiliation: | Departmento de Biología, Facultad de Ciencias, Universidad Autónoma de Madrid 28049 Madrid, Spain |
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Abstract: | The Cyanobacterium Anabaena variabilis ATCC 29413 grown at lowCO2 concentration under mixotrophic conditions with fructoseshowed a repression in the ability to fix inoganic carbon. Thisrepression was not due to a diminution in the ability to transportexternal inorganic carbon but could be explained by a decreaseof two enzymatic activities involved in the assimilation ofinorganic carbon: carbonic anhydrase and Rubisco. Carbonic anhydraseactivity was close to 50% lower in mixotrophic than in autotrophiccells. Moreover growth under mixotrophic conditions reducedRubisco activity at all dissolved inorganic carbon concentrationsassayed (560 mM). Maximum Rubisco activity (Vmax decreasedfrom µmol CO2 mg protein-1h-1 in autotrophic cells to2.3 µmol CO2 mg protein-1h-1 in mixotrophic cells. Nosignificant differences in Km(C1) between autotrophic and mixotrophiccells were however observed. The possible mechanisms involvedin the inhibition of Rubisco are discussed. (Received November 8, 1994; Accepted October 12, 1995) |
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