Carbonic Anhydrase Induction Research Articles

Functional Involvement of Carbonic Anhydrase in the Lysosomal Response to Cadmium Exposure in Mytilus galloprovincialis Digestive Gland.

Carbonic anhydrase (CA) is a ubiquitous metalloenzyme, whose functions in animals span from respiration to pH homeostasis, electrolyte transport, calcification, and biosynthetic reactions. CA is sensitive to trace metals in a number of species. In mussels, a previous study demonstrated CA activity and protein expression to be enhanced in digestive gland by cadmium exposure. The aim of the present work was to investigate the functional meaning, if any, of this response. To this end the study addressed the possible involvement of CA in the lysosomal system response of digestive gland cells to metal exposure. The in vivo exposure to acetazolamide, specific CA inhibitor, significantly inhibited the acidification of the lysosomal compartment in the digestive gland cells charged with the acidotropic probe LysoSensor Green D-189, demonstrating in vivo the physiological contribution of CA to the acidification of the lysosomes. Under CdCl2 exposure, CA activity significantly increased in parallel to the increase of the fluorescence of LysoSensor Green charged cells, which is in turn indicative of proliferation and/or increase in size of lysosomes. Acetazolamide exposure was able to completely inhibit the cadmium induced Lysosensor fluorescence increase in digestive gland cells. In conclusion, our results demonstrated the functional role of CA in the lysosomal acidification of Mytilus galloprovincialis digestive gland and its involvement in the lysosomal activation following cadmium exposure. CA induction could physiologically respond to a prolonged increased requirement of H+ for supporting lysosomal acidification during lysosomal activation.

Functional characterization of neuroendocrine regulation of branchial carbonic anhydrase induction in the euryhaline crab Callinectes sapidus.

Carbonic anhydrase (CA) plays an essential role as a provider of counterions for Na(+)/H(+) and Cl(-)/HCO3 (-) exchange in branchial ionic uptake processes in euryhaline crustaceans. CA activity and gene expression are low in crabs acclimated to full-strength seawater, with transfer to low salinity resulting in large-scale inductions of mRNA and subsequent enzyme activity in the posterior ion-regulating gills (e.g., G7). In the green crab Carcinus maenas, CA has been shown to be under inhibitory neuroendocrine control by a putative hormone in the x-organ-sinus gland complex (XOSG), located in the eyestalk. This study characterizes the neuroendocrine regulation of CA induction in the blue crab Callinectes sapidus, a commonly used experimental organism for crustacean osmoregulation. In crabs acclimated to full-strength seawater, eyestalk ligation (ESL) triggered a 1.8- and 100-fold increase in CA activity and mRNA, respectively. Re-injection with eyestalk homogenates abolished increases in CA activity and fractionally reduced CA gene expression. ESL also enhanced CA induction by 33% after 96 h in crabs transferred to 15 ppt salinity. Injection of eyestalk homogenates into intact crabs transferred from 35 to 15 ppt diminished by 43% the CA induction stimulated by low salinity. These results point to the presence of a repressor hormone in the eyestalk. Separate injections of medullary tissue (MT) and sinus gland (SG), two components of the eyestalk, reduced salinity-stimulated CA activity by 22% and 49%, suggesting that the putative repressor is localized to the SG. Crabs injected with SG extract harvested from crabs acclimated to 5 ppt showed no decrease in CA activity, demonstrating that the hormone is down-regulated at low salinity. Our results show the presence in the XOSG of an inhibitory compound that regulates salinity-stimulated CA induction.

Carbonic anhydrase induction in euryhaline crustaceans is rate-limited at the post-transcriptional level

The transfer of euryhaline crustaceans from full-strength seawater to low salinity results in both a rapid up-regulation of carbonic anhydrase (CA; EC 4.2.1.1) mRNA and a slow induction of CA activity. There is a delay of several days between the two processes, which is attributed to the time required to synthesize new enzyme. These delays may also be due to limitations in the cellular uptake of Zn, which is a required post-translational active site modification to CA. To investigate these processes, the euryhaline crabs, Callinectes sapidus and Carcinus maenas, were acclimated to salinities below their isosmotic points (22.5 and 25ppt, respectively) for 7days to activate the physiological and molecular mechanisms of osmoregulation. CA mRNA increased 90-fold in C. sapidus and 2-fold in C. maenas within 6h; whereas it took 48h for the initial increases in CA activity (120% and 31%), and 4 to 7days for new acclimated levels (300% and 100%, respectively). Crabs were then transferred to lower salinities (10 and 15ppt) to induce further CA activity and to determine if previous increases in CA mRNA reduced the time required for subsequent CA induction. Additionally, the expression of the Zn transporter ZIP1 was examined in C. sapidus at 35 and 22.5ppt. In both species, prior CA mRNA elevation failed to accelerate the rate of CA induction. Levels of CA mRNA did not change in either crab following transfer from intermediate to low salinity. Taken together, these results show that the timecourse of CA induction at low salinity is not limited by the expression of CA mRNA, but by the synthesis of new enzyme from an existing pool of mRNA. No increases in ZIP1 expression occurred at low salinity, therefore these delays may be due to the limits of cellular Zn uptake.

Branchial carbonic anhydrase activity and ninhydrin positive substances in the Pacific white shrimp, Litopenaeus vannamei, acclimated to low and high salinities

The Pacific white shrimp, Litopenaeus vannamei, acclimated to 30 ppt salinity, was transferred to either low (15 and 5 ppt), or high (45 ppt) salinity for 7 days. Hemolymph osmolality, branchial carbonic anhydrase activity, and total ninhydrin-positive substances (TNPS) in abdominal muscle were then measured for each condition. Hemolymph osmotic concentration was regulated slightly below ambient water osmolality in shrimp acclimated to 30 ppt. At 15 and 5 ppt, shrimp were strong hyper-osmotic regulators, maintaining hemolymph osmolality between 200 and 400 mOsm above ambient. Shrimp acclimated to 30 ppt and transferred to 45 ppt salinity were strong hypo-osmotic and hypo-ionic regulators, maintaining hemolymph osmolality over 400 mOsm below ambient. Branchial carbonic anhydrase (CA) activity was low (approximately 100 micromol CO(2) mg protein(-1) min(-1)) and uniform across all 8 gills in shrimp acclimated to 30 ppt, but CA activity increased in all gills after exposure to both low and high salinities. Anterior gills had the largest increases in CA activity, and levels of increase were approximately the same for low and high salinity exposure. Branchial CA induction appears to be functionally important in both hyper- and hypo-osmotic regulations of hemolymph osmotic concentrations. Abdominal muscle TNPS made up between 19 and 38% of the total intracellular osmotic concentration in shrimp acclimated to 5, 15, and 30 ppt. TNPS levels did not change across this salinity range, over which hemolymph osmotic concentrations were tightly regulated. At 45 ppt, hemolymph osmolality increased, and muscle TNPS also increased, presumably to counteract intracellular water loss and restore cell volume. L. vannamei appears to employ mechanisms of both extracellular osmoregulation and intracellular volume regulation as the basis of its euryhalinity.

Quantitative changes in branchial carbonic anhydrase activity and expression in the euryhaline green crab,Carcinus maenas, in response to low salinity exposure

Hemolymph osmolality, and changes in gill carbonic anhydrase (CA) activity, relative mRNA expression, and CA protein concentration were measured in the green crab Carcinus maenas acclimated to 32 ppt salinity and transferred to 10 ppt. Hemolymph osomolality stabilized at new, acclimated values, by 24 hr after transfer. There was a large increase in CA mRNA concentrations, as measured by quantitative PCR, in the posterior gills by 24 hr post-transfer that remained elevated through 4 days. By 7 days, however, CA mRNA levels began to decline. CA activity, on the other hand, did not begin to increase until 48 hr after transfer to 10 ppt, but it continued to increase through 7 days. CA protein concentration increased by 5-fold in posterior gills in crabs acclimated to 10 ppt. CA activity, mRNA expression, and CA protein concentrations did not change in anterior gills. These results indicate that low salinity-stimulated CA induction is under transcriptional regulation, and that the increase in CA activity is a result of the increase in gene expression and synthesis of new enzyme. Changes in mRNA appear to be transient, but once synthesized, the CA protein appears to persist in the gill for an extended time. In a separate set of experiments, green crabs acclimated to 32 ppt were transferred directly to salinities of 25, 20, 15, and 10 ppt. CA activity and mRNA concentrations increased with decreasing salinity, peaking at 15 ppt but decreasing between 15 and 10 ppt. The decrease may represent a breakdown in the mechanism of transport-related protein induction near the lower salinity limit of this species.

Neuroendocrine regulation of carbonic anhydrase expression in the gills of the euryhaline green crab,Carcinus maenas

The relationship between branchial carbonic anhydrase (CA) activity, CA gene expression and salinity, and potential mechanisms of regulation, was investigated in the euryhaline green crab, Carcinus maenas, acclimated to 33 ppt and transferred to 10 ppt, and the stenohaline rock crab, Cancer irroratus, acclimated to 32 ppt and transferred to 18 ppt. CA activity in green crabs acclimated to high and low salinity was a function of CA mRNA expression, with low salinity exposure resulting in an increase in both CA expression and activity. Eyestalk ablation (ESA) in green crabs acclimated to high salinity resulted in an increase in CA expression in the posterior, ion-transporting gills, in the absence of the low salinity stimulus. There were no changes in CA activity or expression in the anterior, respiratory gills. ESA also potentiated low salinity-stimulated CA induction, again, only in posterior gills. There were no changes in CA activity in any gills of Cancer irroratus, in response to either ESA or low salinity. These results suggest that CA expression in euryhaline, osmoregulating species, is under inhibitory regulation by a putative repressor found in the eyestalk, and that this mechanism is absent in stenohaline, osmoconforming species. CA expression is maintained at low, baseline levels in crabs acclimated to high salinity by the presence and action of this compound. The effects of the repressor appear to be reduced upon exposure to low salinity, allowing CA induction to occur.

Effects of eyestalk ablation on carbonic anhydrase activity in the euryhaline blue crabCallinectes sapidus: neuroendocrine control of enzyme expression

Carbonic anhydrase (CA) activity in the gills of the euryhaline blue crab, Callinectes sapidus, was measured in response to acute low-salinity transfer and treatment with eyestalk ablation (ESA) in an attempt to elucidate potential regulatory mechanisms of salinity-mediated CA induction. ESA alone resulted in an approximate doubling of CA activity in the posterior, ion-transporting gills of crabs acclimated to 35 ppt. Transfer of intact crabs to 28 ppt, a salinity at which the blue crab is still an osmotic and ionic conformer, had no effect on CA activity, but treatment with ESA prior to transfer resulted in a 5-fold increase. Hemolymph osmolality was unaffected by ESA. There was a 7-fold induction of CA activity in posterior gills of intact crabs transferred from 35 to 15 ppt, and this was potentiated by about 100% by ESA. Hemolymph osmolality was slightly elevated in the ESA-treated crabs. CA activity in anterior gills did not increase in response to any treatment. Hemolymph concentrations of methyl farnesoate (MF) were measured for all experimental animals. MF concentrations were undetectable in all intact crabs, regardless of salinity. Treatment with ESA resulted in elevated levels of hemolymph MF, but these levels were still relatively low and unrelated to salinity. These results suggest that CA induction is under the control of a regulatory substance located in the eyestalk. This substance appears to be a CA repressor, keeping CA expression at low levels in the gills of crabs acclimated to high salinity. Exposure to low salinity, or treatment with ESA, removes the effects of this putative repressor and allows CA induction to occur.

Critical salinity, sensitivity, and commitment of salinity-mediated carbonic anhydrase induction in the gills of two euryhaline species of decapod crustaceans

Two euryhaline species of decapod crustaceans, Carcinus maenas and Callinectes sapidus, were subjected to a series of acute low-salinity challenges, and changes in carbonic anhydrase (CA) activity in the gills were monitored in order to characterize the nature of salinity-sensitive CA induction. CA activity is uniformly low in all gills of both species at high salinity, but at a critical salinity of 27 ppt, CA induction occurs in the posterior, ion-transporting gills, with CA activity approximately doubling. This salinity occurs right at, or slightly above, the point at which these species make the transition from osmoconformity to osmoregulation. The regulatory mechanism that controls the levels of CA expression after the initial induction has occurred is also very sensitive. Changes in CA activity occur in response to changes in salinity as small as 20 milliosmoles. CA induction only occurs after a critical minimum amount of time of exposure to low salinity (48-72 hr in C. maenas and 12 hr in C. sapidus), but once induction is begun, it continues regardless of subsequent salinity changes. The timing is most likely due to the time it takes for changes in gene expression and resultant increases in CA mRNA to occur in response to low-salinity exposure, and the delay in CA induction could be an adaptation to avoid making metabolically expensive responses to potentially short-term environmental changes.

Salinity-mediated carbonic anhydrase induction in the gills of the euryhaline green crab, Carcinus maenas

The euryhaline green crab, Carcinus maenas, is a relatively strong osmotic and ionic regulator, being able to maintain its hemolymph osmolality as much as 300 mOsm higher than that in the medium when the crab is acclimated to low salinity. It makes the transition from osmoconformity to osmoregulation at a critical salinity of 26 ppt, and new acclimated concentrations of hemolymph osmotic and ionic constituents are reached within 12 h after transfer to low salinity. One of the central features of this transition is an 8-fold induction of the enzyme carbonic anhydrase (CA) in the gills. This induction occurs primarily in the cytoplasmic pool of CA in the posterior, ion-transporting gills, although the membrane-associated fraction of CA also shows some induction in response to low salinity. Inhibition of branchial CA activity with acetazolamide (Az) has no effect in crabs acclimated to 32 ppt but causes a depression in hemolymph osmotic and ionic concentrations in crabs acclimated to 10 ppt. The salinity-sensitive nature of the cytoplasmic CA pool and the sensitivity of hemolymph osmotic/ionic regulation to Az confirm the enzyme's role in ion transport and regulation in this species. CA induction is a result of gene activation, as evidenced by an increase in CA mRNA at 24 h after transfer to low salinity and an increase in protein-specific CA activity immediately following at 48 h post-transfer. CA gene expression appears to be under inhibitory control by an as-yet unidentified repressor substance found in the major endocrine complex of the crab, the eyestalk.

Activation of carbonic anhydrase in branchial cavity tissues of lobsters ( Homarus gammarus) by dilute seawater exposure

Activities of carbonic anhydrase (CA) and its distribution in the branchial cavity tissues were studied in European lobsters ( Homarus gammarus) from ambient seawater (SW; salinity=38 ppt, 1126 mosmol/l) and acclimated to dilute seawater (DSW; salinity=20 ppt, 548 mosmol/l). Acetazolamide inhibited dose dependently the activity of CA in homogenates of epipodites, where the inhibition constant (IC 50=0.12 μM) did not differ significantly from that of membrane vesicles and cytosolic fraction. In DSW-acclimated lobsters, almost 70% of total CA in tissues of the branchial cavity was found in epipodites (E) and the rest was equally distributed between branchiostegites (B) and gills (G). Upon acclimation to dilute seawater, CA activity in membrane fractions of E and B was increased 6-fold and in homogenates, respectively 5- and 13-fold compared to SW-acclimated lobsters. Exposure to DSW enhanced cytosolic CA in E (8-fold) and B (7-fold) over SW-acclimated animals. Slight activation of CA in homogenates and in partially purified membranes of G was not confirmed as a statistically significant difference between SW and DSW groups. In DSW, cytosol specific activity of CA was increased compare to the SW cytosol. These results indicate the importance of E and B in CA induction when lobsters are acclimated to DSW. In subcellular fractions from DSW-acclimated lobsters, the main proportion of 75.8% (E), 61.0% (B) of total CA activity in each of these tissues remained in cytosol portion. Partially purified membranes contained 6.8% (E) and 16.2% (B) and the remainder of 15% (E) and 27% (B) was found in mitochondrial and nuclear fractions. In gills, 49.2% and 9.0 % of total gill CA activity was found respectively in cytosol and partially purified vesicles and the rest in mitochondrial and nuclear fractions.

Early carbonic anhydrase induction in the gills of the blue crab, Callinectes sapidus, during low salinity acclimation is independent of ornithine decarboxylase activity.

Carbonic anhydrase (CA) induction in the gills of the euryhaline blue crab, Callinectes sapidus, was measured in response to lowered environmental salinity. Simultaneous measurements of ornithine decarboxylase (ODC) activity were made in gills and nonbranchial tissues to determine whether ODC activity and the resultant synthesis of polyamines played a role in the initiation and regulation of CA induction. CA induction in the seventh gill pair (G7) was proportional to the decrease in ambient salinity, but activity in the third gill pair (G3) remained unchanged. Induction began by 24 hr after low salinity transfer, much earlier than previously reported, and peaked after 4 days. The magnitude of salinity change affected the magnitude of CA induction only, not the time course. A general cell volume regulatory response, as measured by the appearance of total ninhydrin-positive substances (TNPS) in the hemolymph, was initiated within 4 hr of low salinity transfer and was complete by 24 hr post-transfer. General cell swelling may be the initial signal in the pathway of CA induction. ODC activity in the gills of acclimated animals was not influenced by salinity. For crabs transferred from 35 to 25 ppt, ODC activity did not change significantly over the time course of acclimation. There was an early but transient increase in ODC activity in all tissues for crabs acclimated to 28 ppt and transferred to 15 ppt. Induction of ODC activity does not appear to be a precursor for CA induction; therefore, it does not appear that polyamines are substantially involved in the up-regulation of transport enzyme activity in low salinity. ODC, and resultant polyamine synthesis, may, however, have a role in cell volume regulation.

Environmentally mediated carbonic anhydrase induction in the gills of euryhaline crustaceans.

The enzyme carbonic anhydrase appears to be a central molecular component in the suite of physiological and biochemical adaptations to low salinity found in euryhaline crustaceans. It is present in high activities in the organs responsible for osmotic and ionic regulation, the gills, and more specifically, the individual gills that are specialized for active ion uptake from dilute sea water. Within those gills carbonic anhydrase is distributed among different subcellular pools, the cytoplasm, mitochondria and microsomes. The cytoplasmic pool represents the largest subcellular fraction of carbonic anhydrase activity, and it is this fraction that undergoes a tenfold induction during acclimation to low salinity. Carbonic anhydrase activity is present in excess of that needed to support the general ion-transport processes, and so it is doubtful that carbonic anhydrase activity itself is a point of short-term regulation in response to salinity changes. Rather, upregulation of carbonic anhydrase appears to be a result of selective gene expression, representing a permanent response to long-term adaptation to low salinity. The exact signal that initiates the induction of carbonic anhydrase, and the pathway through which that signal is transduced to the activation of the carbonic anhydrase gene, are unknown, but two promising avenues of research exist. First, induction of carbonic anhydrase is immediately preceded by hemodilution and subsequent cell swelling, a potential initiating event in the process. Second, recent work indicates that expression of carbonic anhydrase is under the control of a repressor substance, located in the eyestalk, whose effect is removed upon exposure to low salinity.

Carbonic anhydrase is induced prior to arylsulfatase under the simultaneous deprivation of inorganic carbon and sulfate in Chlamydomonas reinhardtii (Volvocales, Chlorophyta)

SUMMARYThe activity of periplasmic arylsulfatase (Ars), which catalyzes the cleavage of sulfate from aromatic sulfur compounds, was detected in cells acclimated to the sulfate‐deficient conditions in a unicellular green alga Chlamydomonas reinhardtii Dangeard, but not in Chlorella, Scenedesmus, Dunaliella and Porphyridium. Upon the transfer of cells to sulfate‐deficient autotrophic media under high‐CO2 conditions, the induction of Ars was observed only in the light, but not in the light with dichlorophenyldimethylurea (DCMU) nor in the dark. However, Ars was induced in the light with DCMU or in the dark when acetate was present as an organic carbon source, but not citrate. Under similar high‐CO2 conditions, high‐CO2 requiring mutants of cia‐3 and cia‐5, whose photosynthetic activities are greatly limited under low CO2, showed much lower level of Ars activities than wild type cells. Under Iow‐CO2 conditions the induction of Ars was greatly suppressed even in wild type and no induction was observed in both mutants. These results suggest that the stimulation of photosynthetic or respiratory carbon metabolism are necessary for the induction of Ars. In contrast, the induction of periplasmic carbonic anhydrase (CA) which was synthesized de novo specifically under CO2‐limited conditions was strongly suppressed by the addition of organic carbon sources, such as acetate and citrate. When cells are subjected to CO2‐limitation and sulfate‐deficiency simultaneously, the induction of CA was initiated immediately, while that of Ars was initiated following the completion of CA induction with an about 4‐h lag. When the concentration of CO2 was suddenly lowered during the induction of Ars, the induction of Ars ceased quickly, and the induction of CA was initiated instead. From these results the induction of CA was suggested to have priority over that of Ars under the dual stress of CO2, and sulfate‐deprivation.

Involvement of photorespiration and glycolate pathway in carbonic anhydrase induction and inorganic carbon concentration in Chlamydomonas reinhardtii

Interaction between induction of carbonic anhydrase (CA) activity, induction of inorganic carbon (Ci) concentrating mechanisms and the photorespiratory glycolate pathway has been studied in wild type 6145c and photorespiratory mutant 18–7F (low in phosphoglycolate phosphatase activity) cells of C. reinhardtii. Cell transfer from high CO2 (5%, v/v) to low CO2 (0.03%) provoked an increase of extracellular and total (extracellular plus intracellular) CA in both wild type and mutant cells. During adaptation to low CO2 conditions, both strains excreted ammonium to the medium at a similar rate in the presence of l‐methionine‐d‐l‐sulfoximine (MSX), an inhibitor of glutamine synthetase (GS). MSX also provoked ammonium excretion by air adapted wild type and mutant cells, even though both strains had high levels of CA activity and of Ci concentrating activities.GS increased in both strains after transfer from high to low CO2 conditions. However, this increase was abolished by aminooxyacetate, an inhibitor of the glyoxylate‐serine aminotransferase, and by glycolaldehyde, an inhibitor of triose phosphate to ribulose 1,5‐bisphosphate conversion. CA synthesis did not occur in the presence of either aminooxyacetate or glycolaldehyde. Algae grown in high CO2 in the presence of aminooxyacetate did not induce Ci concentrating mechanisms. Integration of these three processes, i.e., CA synthesis, Ci‐concentration, and photorespiratory glycolate pathway is proposed in the framework of carbon metabolism of the alga.

Involvement of photorespiration and glycolate pathway in carbonic anhydrase induction and inorganic carbon concentration in Chlamydomonas reinhardtii

Involvement of photorespiration and glycolate pathway in carbonic anhydrase induction and inorganic carbon concentration in Chlamydomonas reinhardtii

Effect of Metabolites on Carbonic Anhydrase Induction in Chlorella regularis

Summary When Chlorella regularis cells grown in air enriched with 3% CO 2 were transferred to ordinary air, an increase in carbonic anhydrase (CA) activity, located on the cell surface, was observed. The CA induction was strongly suppressed by the addition of glucose and acetate, and about 40% by glycine. When 4 mM glucose was added, CA induction was suppressed for the first 2 h. But the suppression gradually diminished apparently in correlation with the consumption of glucose added externally. Glucose at 0.5 mM was enough to suppress CA induction completely, and 50% suppression was obtained at almost 0.1 mM. Two millimolar L-methionine sulfoximine, 1 mM aminooxyacetate, and 1.8 mM α-hydroxypyridinemethane sulfonate (α-HPMS) suppressed CA induction completely, 20% and 50%, respectively. The suppression by α-HPMS was not removed by the simultaneous addition of 14.4 mM glyoxylate. These results suggest that CA induction under low CO 2 is reversibly controlled by metabolites and also regulated by the operation of the glycolate pathway and the photorespiratory nitrogen cycle.

Synthesis of carbonic anhydrase with messenger RNA isolated from the cells of Chlamydomonas reinhardtii Dangeard C-9 grown in high and low CO 2

Poly(A) +RNA was isolated from Chlamydomonas reinhardtii cells grown autotrophically in ordinary air (low-CO 2 cells) and in air enriched with 4% CO 2 (high-CO 2 cells). In vitro translation products with the messenger RNA showed that the synthesis of the 37-kDa peptide was greater in low-CO 2 than in high-CO 2 cells. The immunoprecipitate produced by treating the translation products with antiserum against carbonic anhydrase (CA) from this alga was also 37 kDa. Comparison of radioactivities incorporated into these 37 kDA peptides suggested that CA induction by lowering atmospheric CO 2 concentration is regulated at the transcriptional level.

Factors Controlling Induction of Carbonic Anhydrase and Efficiency of Photosynthesis in Chlorella vulgaris llh Cells

When Chlorella vulgaris llh cells which had been grown in air enriched with 2–4% CO2 (high-CO2 cells) were bubbled with air containing ca. 400 ppm CO2, illumination at an intensity as low as the light compensation point (350 lux) was sufficient to increase the photosynthetic rate under limiting CO2 concentrations. The same treatment induced carbonic anhydrase (CA) activity. The induction of CA activity and increase in photosynthetic rate at limiting CO2 concentrations were observed in the presence of 10 μM DCMU which completely inhibits photosynthesis. These results indicate that photosynthetic electron transport is not involved in CA induction in Chlorella vulgaris llh cells. The parallelism between the changes in CA activity and the rate of photosynthesis under limiting CO2 concentrations agree with the previous conclusion that the transport of CO2 from outside to the site of CO2 fixation is facilitated by CA and hence lowers the apparent Km(CO2) for photosynthesis.

Carbonic anhydrase: chemistry, physiology, and inhibition.

Carbonic anhydrase: chemistry, physiology, and inhibition.