ABSTRACT: Localization of lumenal carbonic anhydrase Cah3 in thylakoid membranes of Chlamydomonas reinhardtii was studied using wild-type algae and photosynthetic mutants with different composition of chlorophyll-protein complexes
in the photosystems. In addition, the photosynthetic characteristics of wild-type C. reinhardtii and cia3 mutants lacking the activity of carbonic anhydrase Cah3 were examined. Western blot analysis revealed the lack of cross reaction
with antibodies to Cah3 in the mutant lacking the photosystem II (PSII) reaction center, in contrast to the mutant deficient
in light-harvesting complex of PSII. These data show that the lumenal Cah3 is associated with polypeptides on the donor side
of PSII reaction center. Using immunoelectron microscopy and antibodies to Cah3 from C. reinhardtii, we showed for the first time that the major part of thylakoid Cah3 is localized in the pyrenoid where the bulk of Rubisco
is located. The rate of photosynthetic oxygen evolution and PSII photochemical efficiency were lower in C. reinhardtii cia3 mutant than in the wild type, especially in the cells grown at limiting CO2 concentrations. These observations show that Cah3 takes part in CO2-concentrating mechanism of the chloroplast. The results support our hypothesis [1, 2] that the carboxylation reaction in
microalgae proceeds in the pyrenoid, a specific Rubisco-containing part of the chloroplast, which acquires CO2 from the lumen of intrapyrenoid thylakoids. We discuss significance of the pyrenoid as an autonomous metabolic microcompartment,
in which Cah3 plays a key role in the production and concentration of CO2 for Rubisco. These functions may promote the photosynthetic efficiency owing to the effective CO2 supply for the Calvin cycle.
Russian Journal of Plant Physiology 04/2012; 56(6):761-768. · 0.71 Impact Factor
ABSTRACT: The bases of modern type biosphere were laid down about two billion years ago during the predominance of prokaryotes on the
Earth. Cyanobacteria changed radically the composition of the Proterozoic atmosphere by saturating it with photosynthetic
oxygen. At the same time, large quantities of atmospheric CO2 became sequestered in carbonates owing to mineralization of ancient cyano-bacterial communities; the latter have reached
us in the form of laminated limestone deposits, termed stromatolites. The mechanism of carbonate depositing by cyanobacteria
is still poorly understood. It is not yet clear whether physiological processes are involved in cell mineralization or if
the outer membranes of cyanobacteria serve as a kind of crystallization center and arrange the structure for natural accumulation
of sediments. We proposed that a key role in the mechanism of biomineralization belongs to the enzyme carbonic anhydrase (CA),
which regulates the equilibrium between the inorganic carbon forms (Ci), including bicarbonate that participates in natural sedimentation of calcium. Since the deposition of calcium carbonate
by prokaryotes occurs in the pericellular space and this deposition is controlled by pH, it seems likely that CA, localized
on the periphery of cyanobacterial cells, is involved in stabilizing the external pH and in promoting cell mineralization.
This review summarizes information concerning possible mechanisms of biogenic calcification (CaCO3 deposition). The function of CA in the living cell and the role of this enzyme in biological processes are considered, and
the data on localization of CA in cyano-bacterial cells are presented. Based on available evidence, a scheme is suggested
to describe the role of extracellular CA in photosynthetic carbon assimilation and to relate this process with CaCO3 deposition during mineralization of cyanobacteria.
Russian Journal of Plant Physiology 04/2012; 58(2):197-209. · 0.71 Impact Factor
ABSTRACT: The activity of carbonic anhydrase (CA) was studied in different cell fractions of the alkaliphilic cyanobacterium Microcoleus chthonoplastes. The activity of this enzyme was found in the soluble and membrane protein fractions, as well as in intact cells and in a thick glycocalyx layer enclosing the cyanobacterium cells. The localization of CA in glycocalyx of M. chthonoplastes was shown by western blot analysis and by immunoelectron microscopy studies with antibodies to the thylakoid CA from Chlamydomonas reinhardtii (Cah3). At least one of the CA forms occurring in M. chthonoplastes CA was shown to be an -type enzyme. A possible mechanism of the involvement of the glycocalyx CA in calcification of cyanobacteria is discussed.
Microbiology 01/2004; 73(3):255-259. · 3.06 Impact Factor
ABSTRACT: The activity and intracellular partition of carbonic anhydrase (CA) were studied in alkalophilic cyanobacteria, an inhabitant of soda lakes at pH 9–10. In the homogenates of Rhabdoderma lineare, Rhabdoderma sp., and Microcoleus chthonoplastes, high activity of CA was found, similar to that in eukaryotic microalgae. The activity of CA calculated on the basis of chlorophyll and protein was higher for the soluble (sCA) than for membrane (mCA) protein fraction. Intact cells of all cyanobacteria under investigation also showed CA activity that implies the presence of extracellular form(s). The extracellular CA in benthic M. chthonoplastes was localized, at least partly, in a vast glycocalix (gCA) as shown by Western blotting and the measurement of enzyme activity in the isolated glycocalix preparations. Probing gCA from M. chthonoplastes with the antibodies against thylakoid CA from Chlamydomonas reinhardtii (Cah3) demonstrated that gCA belongs to the -type of enzyme and has the structure identical to that of Cah3. The extracellular CA of M. chthonoplastes manifested the maximum activity at pH 7 and 10, but not at pH 6 and 9. An increase in medium pH from 7.2 to 9.6 resulted only in slight alkalization of the cytoplasm in R. lineare, from 7.1 to 7.5. It follows that true alkalophils can maintain the pH inside the cell at the near-neutral level in spite of high pH (10.2) level in the cultural medium.
Russian Journal of Plant Physiology 06/2003; 50(4):532-539. · 0.71 Impact Factor
ABSTRACT: The partitioning of carbonic anhydrase (CA) activity in chloroplasts isolated from 10–14-day-old pea (Pisum sativum L.) seedlings was investigated. The effect of CA inhibitors on the kinetics of chlorophyll fluorescence in photosystem II (PSII) preparations was also studied. The activity of CA was detected in fractions of soluble proteins and in the polypeptide complexes of the PSI and PSII. Isolated particles of photosystems retained a high photochemical activity similar to that of intact chloroplasts and the high level of polyunsaturated fatty acids. The association of CA with the particles of PSII (PSII-CA) was also tested by Western-blot analysis using antibodies against PSII-CA (Cah3) from Chlamydomonas reinhardtii. The PSII particles isolated with Triton X-100 (T-20) showed a higher activity of the enzyme as calculated on a protein basis than the DT-20 particles isolated with digitonin and Triton X-100. This difference seems to be related to the higher degree of nativity of the chloroplast T-20 fragments as compared to DT-20 particles. The higher level of chlorophyll per reaction center as well as the higher content of chlorophyll b and lipid fatty acids as calculated on protein basis, in particular of E-16:113 acid, which stabilizes the oligomeric structure of the light-harvesting complex of the PSII, also confirms this suggestion. The activity of CA was not detected in the DT-20 preparations treated with Tris–HCl to eliminate manganese ions. This is likely to indicate that one of the extrinsic polypeptides of PSII exhibits CA activity. Specific inhibitors of CA (acetazolamide and imidazole) inhibited the photoinduced yield of chlorophyll fluorescence (F). This might be determined by damaging the water-oxidizing system or its interaction with the PSII reaction centers. The functional role of PSII-CA for 2-concentrating in carboxylation sites as well as its role in the coupling of light and dark reactions in chloroplasts is discussed.
Russian Journal of Plant Physiology 04/2002; 49(3):303-310. · 0.71 Impact Factor