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1.
In C4 plants carbonic anhydrase catalyzes the critical first step of C4 photosynthesis, the hydration of CO2 to bicarbonate. The maximum activity of this enzyme in C4 leaf extracts, measured by H+ production with saturating CO2 and extrapolated to 25°C, was found to be 3,000 to 10,000 times the maximum photosynthesis rate for these leaves. Similar activities were found in C3 leaf extracts. However, the calculated effective activity of this enzyme at in vivo CO2 concentrations was apparently just sufficient to prevent the rate of conversion of CO2 to HCO3 from limiting C4 photosynthesis. This conclusion was supported by the mass spectrometric determination of leaf carbonic anhydrase activities.  相似文献   

2.
Carbonic anhydrases in plants and algae   总被引:12,自引:1,他引:12  
Carbonic anhydrases catalyse the reversible hydration of CO2, increasing the interconversion between CO2 and HCO3 + H+ in living organisms. The three evolutionarily unrelated families of carbonic anhydrases are designated α-, β-and γ-CA. Animals have only the α-carbonic anhydrase type of carbonic anhydrase, but they contain multiple isoforms of this carbonic anhydrase. In contrast, higher plants, algae and cyanobacteria may contain members of all three CA families. Analysis of the Arabidopsis database reveals at least 14 genes potentially encoding carbonic anhydrases. The database also contains expressed sequence tags (ESTs) with homology to most of these genes. Clearly the number of carbonic anhydrases in plants is much greater than previously thought. Chlamydomonas, a unicellular green alga, is not far behind with five carbonic anhydrases already identified and another in the EST database. In algae, carbonic anhydrases have been found in the mitochondria, the chloroplast thylakoid, the cytoplasm and the periplasmic space. In C3 dicots, only two carbonic anhydrases have been localized, one to the chloroplast stroma and one to the cytoplasm. A challenge for plant scientists is to identify the number, location and physiological roles of the carbonic anhydrases.  相似文献   

3.
Burnell JN  Hatch MD 《Plant physiology》1988,86(4):1252-1256
Bundle sheath cells from leaves of a variety of C4 species contained little or no carbonic anhydrase activity. The proportion of total leaf carbonic anhydrase in extracts of bundle sheath cells closely reflected the apparent mesophyll cell contamination of bundle sheath cell extracts as measured by the proportion of the mesophyll cell marker enzymes phosphoenolpyruvate carboxylase and pyruvate,Pi dikinase. Values of about 1% or less of the total leaf activity were obtained for all three enzymes. The recorded bundle sheath carbonic anhydrase activity was compared with a calculated upper limit of carbonic anhydrase activity that would still permit efficient functioning of the C4 pathway; that is, a carbonic anhydrase level allowing a sufficiently high steady state [CO2] to suppress photorespiration. Even before correcting for mesophyll cell contamination the activity in bundle sheath cell extracts was substantially less than the calculated upper limit of carbonic anhydrase activity consistent with effective C4 function. The results accord with the notion that a deficiency of carbonic anhydrase in bundle sheath cells is vital for the efficient operation of the C4 pathway.  相似文献   

4.
By measuring 18O exchange from doubly labeled CO2 (13C18O18O), intracellular carbonic anhydrase activity was studied with protoplasts and chloroplasts isolated from Chlamydomonas reinhardtii grown either on air (low inorganic carbon [Ci]) or air enriched with 5% CO2 (high Ci). Intact low Ci protoplasts had a 10-fold higher carbonic anhydrase activity than did high Ci protoplasts. Application of dextran-bound inhibitor and quaternary ammonium sulfanilamide, both known as membrane impermeable inhibitors of carbonic anhydrase, had no influence on the catalysis of 18O exchange, indicating that cross-contamination with extracellular carbonic anhydrase was not responsible for the observed activity. This intracellular in vivo activity from protoplasts was inhibited by acetazolamide and ethoxyzolamide. Intracellular carbonic anhydrase activity was partly associated with intact chloroplasts isolated from high and low Ci cells, and the latter had a sixfold greater rate of catalysis. The presence of dextran-bound inhibitor had no effect on chloroplast-associated carbonic anhydrase, whereas 150 micromolar ethoxyzolamide caused a 61 to 67% inhibition of activity. These results indicate that chloroplastic carbonic anhydrase was located within the plastid and that it was relatively insensitive to ethoxyzolamide. Carbonic anhydrase activity in crude homogenates of protoplasts and chloroplasts was about six times higher in the low Ci than in high Ci preparations. Further separation into soluble and insoluble fractions together with inhibitor studies revealed that there are at least two different forms of intracellular carbonic anhydrase. One enzyme, which was rather insoluble and relatively insensitive to ethoxyzolamide, is likely an intrachloroplastic carbonic anhydrase. The second carbonic anhydrase, which was soluble and sensitive to ethoxyzolamide, is most probably located in an extrachloroplastic compartment.  相似文献   

5.
A number of non-green plant tissues have high rates of HCO3-consuming reactions in the cytosol, i.e. C4 dicarboxylic acid production preceding organic acid anion transport into dicarboxylate consuming compartments in N2-fixing root nodules, in lipogenic tissues, and in thermogenic aroid spadices and, in the case of lipogenic tissues, in acetyl CoA incorporation into lipid in plastid stroma. Since inorganic C supply to the cytosol or stroma by decarboxylation reactions, and by transmembrane fluxes, involves only CO2, the HCO3 consumed in the rapid metabolic processes must originate from hydration (hydroxylation) of CO2. Computations based on the first-order rate constant for uncatalysed conversion of CO2 to HCO3 and the most likely in vivo CO2 concentration show that the uncatalysed reaction is possibly adequate to supply the observed HCO3 requirement in the HCO3-consuming compartments. However, carbonic anhydrase activity is well established in legume root nodules, and also appears to occur in aroid spadices. In addition to coping with any heterogeneities in HCO3, consumption in the cytosol, the root nodule activity may be involved in optimizing haemoglobin function. Further work is needed on carbonic anhydrase expression is tissues with rapid HCO3 consumption, especially in view of reports of negligible carbonic anhydrase activity in some non-green plant tissues. Other possible roles of carbonic anhydrase in non-green plant tissues are briefly discussed.  相似文献   

6.
Petronijevic T., Rogers W. P. and Sommerville R. I. 1985. Carbonic acid as the host signal for the development of parasitic stages of nematodes. International Journal for Parasitology15: 661–667. This paper gives results on which may be based an identification of the component of the system CO2 + H2O ai H2CO3 ai H+ HCO3? which acts as the stimulus from the animal host for some nematodes. Using infective juveniles of Nematospiroides dubius and Haemonchus contortus, the effects on exsheathment of (1) low pCO2 values, (2) the presence of carbonic anhydrase in the stimulating medium, and (3) the inhibition of carbonic anhydrase within the juveniles have been examined. The results lead to the suggestion that it is the “readily available” undissociated H2CO3, or H2CO3 + HCO3? which is the critical factor in the stimulus for development. The wide range of [H+]s over which “readily available” H2CO3 is present in physiological environments suggests that this host signal may be important for infection with many species.  相似文献   

7.
Summary Quantitative analysis has been made of the reactions underlying the Hansson histochemical method for carbonic anhydrase, with a view toward resolving controversies that have arisen regarding its application and specificity.The basic event is the loss of CO2 from the surface of solutions containing HCO 3 , PO 4 2– and cobalt at pH 6–8. Displacement of the equilibria H2CO3 CO2 to the right elevates the pH, and at 6.8 a cobalt precipitate is formed. When tissue containing carbonic anhydrase is floated on the surface, the loss of CO2 and elevation of pH is accelerated at the enzyme site, leading to ncreased cobalt deposits. These are converted to cobalt sulphide for visualization.Study of the changes of pH and CO2 equilibria during the reaction point strongly to the fact that enzymic activity is being measured by the cobalt localization. This activity is reduced or abolished by appropriate concentrations of acetazolamide (or other sulphonamide inhibitors of carbonic anhydrase) and the powerful inorganic inhibitor, cyanate (CNO) ion.  相似文献   

8.
A simple model based on HCO3 transport has been developed to relate photosynthesis and inorganic carbon fluxes for the marine cyanobacterium, Synechococcus sp. Nägeli (strain RRIMP N1). Predicted relationships between inorganic carbon transport, CO2 fixation, internal carbonic anhydrase activity, and leakage of CO2 out of the cell, allow comparisons to be made with experimentally obtained data. Measurements of inorganic carbon fluxes and internal inorganic carbon pool sizes in these cells were made by monitoring time-courses of CO2 changes (using a mass spectrometer) during light/dark transients. At just saturating CO2 conditions, total inorganic carbon transport did not exceed net CO2 fixation by more than 30%. This indicates CO2 leakage similar to that estimated for C4 plants.

For this leakage rate, the model predicts the cell would need a conductance to CO2 of around 10−5 centimeters per second. This is similar to estimates made for the same cells using inorganic carbon pool sizes and CO2 efflux measurements. The model predicts that carbonic anhydrase is necessary internally to allow a sufficiently fast rate of CO2 production to prevent a large accumulation of HCO3. Intact cells show light stimulated carbonic anhydrase activity when assayed using 18O-labeled CO2 techniques. This is also supported by low but detectable levels of carbonic anhydrase activity in cell extracts, sufficient to meet the requirements of the model.

  相似文献   

9.
In order to broaden our understanding of the eukaryotic CO2-concentrating mechanism the occurrence and localization of a thylakoid-associated carbonic anhydrase (EC 4.2.1.1) were studied in the green algae Tetraedron minimum and Chlamydomonas noctigama. Both algae induce a CO2-concentrating mechanism when grown under limiting CO2 conditions. Using mass-spectrometric measurements of 18O exchange from doubly labelled CO2, the presence of a thylakoid-associated carbonic anhydrase was confirmed for both species. From purified thylakoid membranes, photosystem I (PSI), photosystem II (PSII) and the light-harvesting complex of the photosynthetic apparatus were isolated by mild detergent gel. The protein fractions were identified by 77 K fluorescence spectroscopy and immunological studies. A polypeptide was found to immunoreact with an antibody raised against thylakoid carbonic anhydrase (CAH3) from Chlamydomonas reinhardtii. It was found that this polypeptide was mainly associated with PSII, although a certain proportion was also connected to light harvesting complex II. This was confirmed by activity measurements of carbonic anhydrase in isolated bands extracted from the mild detergent gel. The thylakoid carbonic anhydrase isolated from T. minimum had an isoelectric point between 5.4 and 4.8. Together the results are consistent with the hypothesis that thylakoid carbonic anhydrase resides within the lumen where it is associated with the PSII complex. Received: 13 May 2000 / Accepted: 16 August 2000  相似文献   

10.
When Dunaliella tertiolecta, previously adapted to medium containing 0.5 M NaCl, is transferred to higher salinities, there is a lag in growth, suggesting an adaptation period. Since there is no significant difference in the Na+ content of cells grown between 0.5 and 3.5 M NaCl, a mechanism for Na+ extrusion or exclusion is indicated. Increasing the salinity of cell suspensions stimulates an incorporation of H+ by the cells, suggesting an H+/Na+ exchange. Cells adapted to higher salinities have, increased carbonic anhydrase activity, suggesting that increased CO2 or HCO3? transport may be required at higher salinities. Growth, of D. tertiolecta at salinities above 2.5 M requires continuous illumination; therefore a light-driven H+/Na+ exchange accompanied by a HCO3? influx is proposed.  相似文献   

11.
The review summarizes current data on the existence in terrestrial higher plants of several carbonic anhydrase forms differing in their properties, molecular structure, and intracellular localization. Possible functions of these carbonic anhydrases are discussed as well as specific features of carbon-concentrating mechanisms in phototrophic tissues of plants with C3 and C4 pathways of photosynthesis.  相似文献   

12.
13.
Distribution of carbonic anhydrase in British marine macroalgae   总被引:8,自引:0,他引:8  
Summary Thirty-four species of marine macroalgae from around St. Andrews, Scotland, have been assayed for their external activity and thirty-three species for their total activity of carbonic anhydrase. Activity was detected in all the Rhodophyta tested apart from Chondrus crispus, but was absent in Codium fragile, Enteromorpha sp. and Monostroma fuscum (Chlorophyta), and Alaria esculenta, Laminaria digitata, L. saccharina and L. hyperborea (Phaeophyta). Total activity of carbonic anhydrase per unit fresh weight tended to be higher in the Rhodophyta than in the Chlorophyta or Phaeophyta. External activity was present in two of the six Chlorophyta, four of the twelve Phaeophyta and four of the sixteen Rhodophyta tested. On average, when present, external carbonic anhydrase activity represented 2.7% of the total activity. A relationship was found between total carbonic anhydrase activity and habitat. Species from the high intertidal and the low-light subtidal habitats had significantly higher activity than species from the mid and low intertidal, rockpools, or high-light region of the subtidal. External carbonic anhydrase activity did not vary significantly with habitat. There appeared to be no strong relationship between carbonic anhydrase activity and the ability of a species to use HCO - 3 in photosynthesis under water.  相似文献   

14.
Active human carbonic anhydrase II (HCAII) protein was expressed in the cyanobacterium Synechococcus PCC7942 by means of transformation with the bidirectional expression vector, pCA. This expression was driven by the bacterial Tac promoter and was regulated by the IacIQ repressor protein, which was expressed from the same plasmid. Expression levels reached values of around 0.3% of total cell protein and this protein appeared to be entirely soluble in nature and located within the cytosol of the cell. The expression of this protein has dramatic effects on the photosynthetic physiology of the cell. Induction of expression of carbonic anhydrase (CA) activity in both high dissolved inorganic carbon (Ci) and low Ci grown cells leads the creation of a high Ci requiring phenotype causing: (a) a dramatic increase in the K0.5 (Ci) for photosynthesis, (b) a loss of the ability to accumulate internal Ci, and (c) a decrease in the lag between the initial Ci accumulation following illumination and the efflux of CO2 from the cells. In addition, the effects of the expressed CA can largely be reversed by the carbonic anhydrase inhibitor ethoxyzolamide. As a result of the above findings, it is concluded that the CO2 concentrating mechanism in Synechococcus PCC7942 is largely dependent on (a) the absence of CA activity from the cytosol, and (b) the specific localization of CA activity in the carboxysome. A theoretical model of photosynthesis and Ci accumulation is developed in which the carboxysome plays a central role as both the site of CO2 generation from HCO3 and a resistance barrier to CO2 efflux from the cell. There is good qualitative agreement between this model and the measured physiological effects of expressed cytosolic CA in Synechococcus cells.  相似文献   

15.
During plant tissue culture, the culture container is small and sealed; the concentration of CO2 in the microenvironment is relatively low. The plantlet growth is restrained for the shortage of CO2 in the culture container. Carbonic anhydrase is a zinc-containing metalloenzyme that catalyzes the reversible conversion of bicarbonate to CO2. The determination of carbonic anhydrase of leaves from Atractylodes lancea (thunb.) DC, Orychophragmus violaceus (L.) O.E. Schulz, Brassica juncea (L.) Czern.et Coss. cv. Luzhousileng, Brassica campestris L. cv. Chuanyou No.8, Brassica napus L cv. Oro, Brassica carinata Braun, Raphanus sativa L. var. raphanistroides Makino and their plantlets indicates that the carbonic anhydrase activity of leaves from both plantlets and fields varies from plant species to plant species, the carbonic anhydrase activity of leaves of Atractylodes lancea (thunb.) DC is the lowest among those plants, and the leaves of all plantlets are lower in carbonic anhydrase activity than the same species of plants from fields. The comparison of the growth rates of those plantlets shows that their relative growth rates are significantly different, plantlets of Atractylodes lancea have the slowest relative growth rate among those plants, and plantlets of Brassica juncea have the greatest relative growth rate. The relationship between RGR of plantlets and their CA activities is a significant linear function. It seems that there was certain correlation between carbonic anhydrase activities of plants and their growth rates. It suggests that in vitro, the greater the carbonic anhydrase activity of plantlet is, the higher its net photosynthetic rate, and the faster its growth rate. Those results offer a foundation to a rational medium choice in plant tissue culture.  相似文献   

16.
Light induced proton efflux in intact cells ofAnabaena flos-aquae is inhibited by the heavy metals Hg2+ and Cd2+. Furthermore, Hg2+ and Cd2+ reduced the14CO2 fixation, oxygen evolution and carbonic anhydrase activity responsible for H+ efflux.  相似文献   

17.
It is known, that the multi-subunit complex of photosystem II (PSII) and some of its single proteins exhibit carbonic anhydrase activity. Previously, we have shown that PSII depletion of HCO3?/CO2 as well as the suppression of carbonic anhydrase activity of PSII by a known inhibitor of α?carbonic anhydrases, acetazolamide (AZM), was accompanied by a decrease of electron transport rate on the PSII donor side. It was concluded that carbonic anhydrase activity was required for maximum photosynthetic activity of PSII but it was not excluded that AZM may have two independent mechanisms of action on PSII: specific and nonspecific. To investigate directly the specific influence of carbonic anhydrase inhibition on the photosynthetic activity in PSII we used another known inhibitor of α?carbonic anhydrase, trifluoromethanesulfonamide (TFMSA), which molecular structure and physicochemical properties are quite different from those of AZM. In this work, we show for the first time that TFMSA inhibits PSII carbonic anhydrase activity and decreases rates of both the photo-induced changes of chlorophyll fluorescence yield and the photosynthetic oxygen evolution. The inhibitory effect of TFMSA on PSII photosynthetic activity was revealed only in the medium depleted of HCO3?/CO2. Addition of exogenous HCO3? or PSII electron donors led to disappearance of the TFMSA inhibitory effect on the electron transport in PSII, indicating that TFMSA inhibition site was located on the PSII donor side. These results show the specificity of TFMSA action on carbonic anhydrase and photosynthetic activities of PSII. In this work, we discuss the necessity of carbonic anhydrase activity for the maximum effectiveness of electron transport on the donor side of PSII.  相似文献   

18.

Background

Cyperus rotundus L. is a C4 weed of large vegetative and reproductive vigor endowed with competitive advantages over most crop species mainly under adverse environmental conditions. Vacuole functions are critical for the mechanisms of drought resistance, and here the modulation of the primary system of vacuolar ion transport is investigated during a transient water stress imposed to this weed and to C4 crop species (Zea mays L.).

Methods

The vacuolar H+ pumps, the H+-ATPase and H+-PPiase, expression, activities and the energy coupling were spectrophotometrically investigated as key elements in the differential drought-resistance mechanisms developed by weeds and crops.

Results

In C. rotundus tonoplasts, ATP hydrolysis was more sensitive to drought than its coupled H+ transport, which was in turn at least 3-folds faster than that mediated by the H+-PPiase. Its PPi hydrolysis was only slightly affected by severe water deficit, contrasting with the disruption induced in the PPi-dependent H+-gradient. This effect was antagonized by plant rehydration as the H+-PPiase activity was highly stimulated, reassuming a coupled PPi-driven H+ pumping. Maize tonoplasts exhibited 2–4 times lower hydrolytic activities than that of C. rotundus, but were able to overactivate specifically PPi-dependent H+ pumping in response to stress relief, resulting in an enhanced H+-pumps coupling efficiency.

Conclusion

These results together with immunoanalysis revealed profiles consistent with pre- and post-translational changes occurring on the tonoplast H+-pumps, which differ between weeds and crops upon water deficit.

General significance

The evidences highlight an unusual modulation of the H+-PPiase energy coupling as a key biochemical change related to environmental stresses adaptive capacity of plants.  相似文献   

19.
Microbial carbonic anhydrase promotes carbonate deposition, which is important in the formation and evolution of global carbon cycle and geological processes. A kind of bacteria producing extracellular carbonic anhydrase was selected to study the effects of temperature, pH value and Ca2+ concentration on bacterial growth, carbonic anhydrase activity and calcification rate in this paper. The results showed that the activity of carbonic anhydrase at 30 °C was the highest, which was beneficial to the calcification reaction, calcification rate of CaCO3 was the fastest in alkaline environment with the initial pH value of 9.0. When the Ca2+ concentration was 60 mM, compared with other Ca2+ concentration, CA bacteria could grow and reproduce best, and the activity of bacteria was the highest, too low Ca2+ concentration would affect the generation of CaCO3, while too high Ca2+ concentration would seriously affect the growth of bacteria and reduce the calcification rate. Finally, the mechanism of CaCO3 precipitation induced by microbial carbonic anhydrase was studied. Carbonic anhydrase can accelerate the hydration of CO2 into HCO3, and react with OH and Ca2+ to form CaCO3 precipitation in alkaline environment and in the presence of calcium source.  相似文献   

20.
The β-carbonic anhydrases (β-CAs) are a diverse but structurally related group of zinc-metalloenzymes found in eubacteria, plant chloroplasts, red and green algae, and in the Archaea. The enzyme catalyzes the rapid interconversion of CO2 and H2O to HCO3 and H+, and is believed to be associated with metabolic enzymes that consume or produce CO2 or HCO3. For many organisms, β-CA is essential for growth at atmospheric concentrations of CO2. Of the five evolutionarily distinct classes of carbonic anhydrase, β-CA is the only one known to exhibit allosterism. Here we review the structure and catalytic mechanism of β-CA, including the structural basis for allosteric regulation.  相似文献   

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