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Carbonic anhydrase in eukaryotic algae: characterization, regulation, and possible function during photosynthesis1
Abstract: Carbonic anhydrase (CA) speeds up the equilibrium between CO^sub 2^ and HCO^sub 3^- at physiological pH values and has been detected in almost every species of the animal and plant kingdoms. Among eucaryotic micro- and macro-algae the enzyme is widely distributed and plays an important role in photosynthetic CO^sub 2^ fixation. In some cases, different forms of carbonic anhydrases located extracellularly and intracellularly have been found to occur in the same cell. The expression of the genes encoding these CA isoforms are under the control of the inorganic carbon concentration in the medium, as the activities increase with decreasing the inorganic carbon content. Considerable progress has been made in recent years in isolating and characterizing the various forms of carbonic anhydrases on a biochemical and molecular level. Most of the data have been collected for microalgae like Chlamydomonas reinhardt (Dangeard), while the situation in macroalgae is still descriptive. Therefore, this review summarizes the recent development with an emphasis on microalgae carbonic anhydrases.
Key words: carbonic anhydrase, CO^sub 2^ concentrating mechanism, macroalgae, microalgae, photosynthesis.
Resume: L'anhydrase carbonique (CA) accelere l'equilibre entre le CO^sub 2^ et le HCO3- h des valeurs de pH physiologiques et a ete decele chez presque toutes les especes animales et vegetales. Chez les micro- et macro-algues eucaryotes,1'enzyme est largement distribue et joue un role important dans la fixation photosynth6tique du CO^sub 2^. Dans certains cas, on a trouve differentes formes d'anhydrases carboniques localis6es dans et hors cellule pour une meme cellule. L'expression des genes codants pour ces isoformes du CA tombent sous le controle de la teneur en carbone inorganique dans le milieu, a mesure que les activites augmentent et que la teneur en carbone inorganique diminue. D'importants progres ont 6t6 realises au cours des r6centes annees en vue d'isoler et de caract6riser les diverses formes d'anhydrases carboniques au niveau biochimique et moleculaire. La plupart des donnees ont ete obtenues a partir de microalgues telles que le Chlamydomonas reinhardt (Dangeard), alors que la situation chez les macroalgues est encore limit6e a la description. Consequemment cette revue fait le sommaire des developpements recents en mettant l'accent sur l'anhydrase carbonique des microalgues.
Mots cles: anhydrase carbonique, mecanisme de...