Compartmentation of α- and -Carbonic Anhydrases in Cells of Halo- and Alkalophilic Cyanobacteria Rhabdoderma lineare

Abstract

The organization of carbonic anhydrase (CA) system in halo- and alkalophilic cyanobacteria Rhabdoderma lineare was studied by Western blot analysis and immunocytochemical electron microscopy. The presence of extracellular α-CA (60 kD) in the glycocalyx, forming a tight sheath around the cell, and of two intracellular β-CA is reported. One β-CA (60 kD) is associated with polypeptides of photosystem II (PSII) and is a constitutive enzyme. Another β-carbonic anhydrase (25 kD) was induced by low content of bicarbonate in the culture medium; this inducible CA was found in the fraction of total soluble proteins. The expressed synthesis of inducible β-CA was accompanied by the increase in the intracellular pool of inorganic carbon, which suggests an important role of this enzyme in the functioning of CO2-concentrating mechanism.