M. Nieva et Ef. Valiente, INORGANIC CARBON TRANSPORT AND FIXATION IN CELLS OF ANABAENA-VARIABILIS ADAPTED TO MIXOTROPHIC CONDITIONS, Plant and Cell Physiology, 37(1), 1996, pp. 1-7
The cyanobacterium Anabaena variabilis ATCC 29413 grown at low CO2 con
centration under mixotrophic conditions with fructose showed a repress
ion in the ability to fix inorganic carbon. This repression was not du
e to a diminution in the ability to transport external inorganic carbo
n but could be explained by a decrease of two enzymatic activities inv
olved in the assimilation of inorganic carbon: carbonic anhydrase and
Rubisco. Carbonic anhydrase activity was close to 50% lower in mixotro
phic than in autotrophic cells. Moreover growth under mixotrophic cond
itions reduced Rubisco activity at all dissolved inorganic carbon conc
entrations assayed (5-60 mM). Maximum Rubisco activity (V-max decrease
d from 4.7 mu mol CO2 mg protein(-1) h(-1) in autotrophic cells to 2.3
mu mol CO2 mg protein(-1) h(-1) in mixotrophic cells. No significant
differences in K-m (C-i) between autotrophic and mixotrophic cells wer
e however observed. The possible mechanisms involved in the inhibition
of Rubisco are discussed.