Levels Of Carbonic Anhydrase Activity Research Articles

Carbonic Anhydrase Robustness for Use in Nanoscale CO2 Capture Technologies.

Continued dependence on crude oil and natural gas resources for fossil fuels has caused global atmospheric carbon dioxide (CO2) emissions to increase to record-setting proportions. There is an urgent need for efficient and inexpensive carbon sequestration systems to mitigate large-scale emissions of CO2 from industrial flue gas. Carbonic anhydrase (CA) has shown high potential for enhanced CO2 capture applications compared to conventional absorption-based methods currently utilized in various industrial settings. This study aims to understand structural aspects that contribute to the stability of CA enzymes critical for their applications in industrial processes, which require the ability to withstand conditions different from those in their native environments. Here, we evaluated the thermostability and enzyme activity of mesophilic and thermophilic CA variants at different temperature conditions and in the presence of atmospheric gas pollutants like nitrogen oxides and sulfur oxides. Based on our enzyme activity assays and molecular dynamics simulations, we see increased conformational stability and CA activity levels in thermostable CA variants incubated week-long at different temperature conditions. The thermostable CA variants also retained high levels of CA activity despite changes in solution pH due to increasing NO and SO2 concentrations. A loss of CA activity was observed only at high concentrations of NO/SO2 that possibly can be minimized with the appropriate buffered solutions.

Determination of chlorophyll content, carbonic anhydrase activity, bio-productivity and composition of groundnuts under five Zinc Oxide (ZnO) applications

The low level of carbonic anhydrase activity in groundnut grown on soil with limited zinc (Zn) content is one of the factors responsible for low yield in groundnuts in Nigeria. Hence, this study was carried out to further strengthen the significance of Zn in enhancing photosynthetic processes through carbonic anhydrase activity. It also determines how Zn application affects biochemical components, growth, yield and composition of Arachis hypogaea cv SAMNUT 22. In this study, a potexperiment was performed to investigate the effects of five concentrations of Zn applied in form of zinc oxide (0.00, 1.00, 2.00, 3.00 and 4.00 gL-1ZnO) on the chlorophyll, carbonic anhydrase activity, bio-productivity and proximate composition of groundnut seeds. Data on the aforementioned parameters were subjected to One-way Analysis of Variance and means separated using Duncan Multiple Range Test at p<0.05. The results showed that total chlorophyll in leaves increased with increasing concentration of ZnO and hence the lowest and highest chlorophyll were recorded in 1.00 gL-1 and 4.00 gL-1 respectively. Carbonic anhydrase, after flowering showed a marked improvement with increases in ZnO application compared to the control. The bio-productivity in terms of growth components and yield attributes were respectively enhanced when the concentration of the applied ZnO is increased. Carbohydrate, protein and ash content of harvested seeds were significantly higher (p<0.05) in ZnO treated plants when compared to the control. The results indicated that application of ZnO at 4.00 gL-1 is considered optimum for enhancement of biochemical, growth and yield attributes of the studied groundnut. Also, the reported concentrations of ZnO showed positive influences only on carbohydrate, protein and ash contents of the harvested seeds.

Blood and Gill Carbonic Anhydrase in the Context of a Chondrichthyan Model of CO2 Excretion.

Pacific spiny dogfish (Squalus suckleyi) have been widely used as a representative species for chondrichthyan CO2 excretion. Pacific spiny dogfish have a slower red blood cell (RBC) carbonic anhydrase (CA) isoform than teleost fishes, extracellular CA activity, no endogenous plasma CA inhibitor, and plasma-accessible CA IV at the gills. Thus, both the RBC and plasma compartments contribute to bicarbonate ion () dehydration at the gills for CO2 excretion in contrast to teleost fishes, in which dehydration is restricted to RBCs. We compared CA activity levels, subcellular localization, and presence of plasma CA inhibitors in the blood and gills of 13 chondrichthyans to examine the hypothesis that the dogfish model of CO2 excretion applies broadly to chondrichthyans. In general, blood samples from the 12 other chondrichthyans examined had lower RBC CA activity than teleosts, some extracellular CA activity, and no endogenous plasma CA inhibitor. While type IV-like membrane-associated CA was found in the gills in all four of the chondrichthyans examined, S. suckleyi had three times more CA activity ( μmol CO2 min-1 mg protein-1) in the microsomal (membrane) fraction of gills than the other three. In addition, unexpected variation in CA characteristics was observed between chondrichthyan species. Thus, in general, it appears that the pattern of CA distribution in fishes can be generally categorized as either chondrichthyan or teleost models. However, further studies should examine the functional significance of the within-chondrichthyan differences we observed and investigate whether CO2 excretion patterns exist along a continuum or in discrete groups.

Carbonic anhydrase activity in seaweeds: overview and recommendations for measuring activity with an electrometric method, using Macrocystis pyrifera as a model species

Carbonic anhydrase (CA) plays an important physiological role in all biological systems by accelerating the interconversion of CO2 and HCO3−. In algae, CA is essential for photosynthesis: external CA (CAext) dehydrates HCO3−, enhancing the supply of CO2 to the cell surface, and internal CA (CAint) interconverts HCO3− and CO2 to maintain the inorganic carbon (Ci) pool and supply CO2 to RuBisCO. We first conducted a literature review comparing the conditions in which CA extraction and measurement have been carried out, using the commonly used Wilbur–Anderson method. We found that the assay has been widely modified since its introduction in 1948, mostly without being optimized for the species tested. Based on the review, an optimized protocol for measuring CA in Macrocystis pyrifera was developed, which showed that the assay conditions can strongly affect CA activity. Tris–HCl buffer gave the highest levels of CA activity, but phosphate buffer reduced activity significantly. Buffers containing polyvinylpyrrolidone (PVP) and dithiothreitol (DTT) stabilized CA. Using the optimized assay, CAext and CAint activities were readily measured in Macrocystis with higher precision compared to the non-optimized method. The CAint activity was 2 × higher than CAext, which is attributed to the Ci uptake mechanisms of Macrocystis. This study suggests that the CA assay needs to be optimized for each species prior to experimental work to obtain both accurate and precise results.

Does assessment of carbonic anhydrase activity support the diagnosis of various thyroid disorders

ObjectiveTo evaluate the activity of carbonic anhydrase (CA) in various thyroid disorder patients and their results were compared with euthyroid acting as a control. MethodsTwo hundred and sixty-three participants were enrolled for the present study with ages ranging from 6 months to 74 years. Among them, hypothyroid, hyperthyroid and euthyroid subjects were chosen. Twelve hours' fasting blood samples were collected from all the patients reported to Medicine Out Patients Department and assessment of CA activity was done in all the three category patients. The data from the patients and controls were compared by using the student's t-test. The values were expressed as mean±standard deviation. Microsoft Excel for Windows 2003 was used for statistical analysis. P<0.05 were considered to indicate statistical significance. ResultsThe serum levels of CA activities were observed to be higher in hyperthyroid patients compared to hypothyroid ones and the CA activity in euthyroid subjects were comparatively higher than hypothyroid subjects. It was also observed that the serum CA activity was significantly correlated with both T4 (r=0.997, P<0.001) and FT4 (r=0.590, P=0.039) values. ConclusionThough our study contains a very small sample size, as a pilot study we have demonstrated that the serum levels of CA activity is associated with the serum thyroxine levels.

Cardiac responses to hypercapnia in larval zebrafish (Danio rerio): the links between CO2 chemoreception, catecholamines and carbonic anhydrase.

The ontogeny of carbon dioxide (CO2) sensing in zebrafish (Danio rerio) has not been examined. In this study, CO2-mediated increases in heart rate were used to gauge the capacity of zebrafish larvae to sense CO2. CO2 is thought to be detected via neuroepithelial cells (NECs), which are homologous to mammalian carotid body glomus cells. Larvae at 5 days post-fertilization (d.p.f.) exhibited tachycardia when exposed for 30 min to 0.75% CO2 (~5.63 mmHg); at 7 d.p.f., tachycardia was elicited by 0.5% CO2 (~3.75 mmHg). Based on pharmacological evidence using β-adrenergic receptor (β-AR) antagonists, and confirmed by β1-AR translational gene knockdown using morpholinos, the reflex tachycardia accompanying hypercapnia was probably mediated by the interaction of catecholamines with cardiac β1 receptors. Because the cardiac response to hypercapnia was abolished by the ganglionic blocker hexamethonium, it is probable that the reflex cardio-acceleration was mediated by catecholamines derived from sympathetic adrenergic neurons. Owing to its likely role in facilitating intracellular acidification during exposure to hypercapnia, it was hypothesized that carbonic anhydrase (CA) is involved in CO2 sensing, and that inhibition of CA activity would blunt the downstream responses. Indeed, the cardiac response to hypercapnia (0.75% CO2) was reduced in fish at 5 d.p.f. exposed to acetazolamide, a CA inhibitor, and in fish experiencing zCAc (CA2-like a) knockdown. Successful knockdown of zCAc was confirmed by CA activity measurements, western blotting and immunocytochemistry. Co-injection of embryos with zCAc morpholino and mRNA modified at the morpholino binding site restored normal levels of CA activity and protein levels, and restored (rescued) the usual cardiac responses to hypercapnia. These data, combined with the finding that zCAc is expressed in NECs located on the skin, suggest that the afferent limb of the CO2-induced cardiac reflex in zebrafish larvae is initiated by coetaneous CO2-sensing neuroepithelial cells.

Carbonic anhydrase and Na/K-ATPase activities during the molt cycle of low salinity-reared white shrimp Litopenaeus vannamei

Changes in hemolymph osmolality, ion concentrations, and enzymatic activities of carbonic anhydrase (CA) in the gills and epidermal tissue, and Na/K-ATPase in the gills during the molt cycle were investigated in the white shrimp Litopenaeus vannamei. Hemolymph osmolality was high in the intermolt and early premolt stages, but started to decrease prior to ecdysis through to postmolt stages A and B. Changes in Na+ and Cl− ion concentrations paralleled those in hemolymph osmolality. CA activity levels in the anterior and posterior gills were low at intermolt stage C0 and premolt stage D0, and maximum at premolt stage D3. In the epidermal tissue, activity was relatively high at intermolt stage C0 and premolt stage D0, but fluctuated towards premolt stage D3 and postmolt stage A. On the other hand, Na/K-ATPase activity in the gills decreased between intermolt stage C0 and premolt stage D2, but increased at premolt stage D3 and postmolt stage A. The changes in patterns of CA activity during the molt cycle suggest that CA may be involved in supplying counter-ions for Na+ and Cl− uptake during molting. Branchial Na/K-ATPase appears to be involved in producing local osmotic gradients in order to support water influx across the epithelium.

Loss of the transit peptide and an increase in gene expression of an ancestral chloroplastic carbonic anhydrase were instrumental in the evolution of the cytosolic C4 carbonic anhydrase in Flaveria.

C(4) photosynthesis has evolved multiple times from ancestral C(3) species. Carbonic anhydrase (CA) catalyzes the reversible hydration of CO(2) and is involved in both C(3) and C(4) photosynthesis; however, its roles and the intercellular and intracellular locations of the majority of its activity differ between C(3) and C(4) plants. To understand the molecular changes underlying the evolution of the C(4) pathway, three cDNAs encoding distinct beta-CAs (CA1, CA2, and CA3) were isolated from the leaves of the C(3) plant Flaveria pringlei. The phylogenetic relationship of the F. pringlei proteins with other embryophyte beta-CAs was reconstructed. Gene expression and protein localization patterns showed that CA1 and CA3 demonstrate high expression in leaves and their products localize to the chloroplast, while CA2 expression is low in all organs examined and encodes a cytosolic enzyme. The roles of the F. pringlei enzymes were considered in light of these results, other angiosperm beta-CAs, and Arabidopsis (Arabidopsis thaliana) "omics" data. All three F. pringlei CAs have orthologs in the closely related C(4) plant Flaveria bidentis, and comparisons of ortholog sequences, expression patterns, and intracellular locations of their products indicated that CA1 and CA2 have maintained their ancestral role in C(4) plants, whereas modifications to the C(3) CA3 gene led to the evolution of the CA isoform that catalyzes the first step in the C(4) photosynthetic pathway. These changes included the loss of the chloroplast transit peptide and an increase in gene expression, which resulted in the high levels of CA activity seen in the cytosol of C(4) mesophyll cells.

Carbonic anhydrase and Na/K-ATPase activities at different molting stages of the giant freshwater prawn Macrobrachium rosenbergii

In the present study, the role of carbonic anhydrase (CA) and Na/K-ATPase in the gill and epidermal tissues in the giant freshwater prawn Macrobrachium rosenbergii was examined as a function of molting stage. CA activity levels in the front and back gills were low at the intermolt stage C0, but increased significantly at premolt stage D3, and then decreased after molting. In the epidermal tissue, activity levels decreased gradually towards premolt to a minimum level at stage D3, but became elevated at postmolt stages A and B. Na/K-ATPase levels in the front and back gills did not change significantly during the molt cycle. CA in the gill is possibly involved in supplying counter-ions for ion uptake, while CA in the epidermal tissue may play a role in mineralizing the exoskeleton after ecdysis. Na/K-ATPase in the gills may function in ion uptake from the ambient medium; however, since its activity was not influenced by the molt cycle, it probably does not have a major role in osmoregulation in the freshwater environment.

A Transgenic Approach to Understanding the Influence of Carbonic Anhydrase on C18OO Discrimination during C4 Photosynthesis

The oxygen isotope composition of atmospheric CO(2) is an important signal that helps distinguish between ecosystem photosynthetic and respiratory processes. In C(4) plants the carbonic anhydrase (CA)-catalyzed interconversion of CO(2) and bicarbonate (HCO(3)(-)) is an essential first reaction for C(4) photosynthesis but also plays an important role in the CO(2)-H(2)O exchange of oxygen as it enhances the rate of isotopic equilibrium between CO(2) and water. The C(4) dicot Flaveria bidentis containing genetically reduced levels of leaf CA (CA(leaf)) has been used to test whether changing leaf CA activity influences online measurements of C(18)OO discrimination (Delta(18)O) and the proportion of CO(2) in isotopic equilibrium with leaf water at the site of oxygen exchange (theta). The Delta(18)O in wild-type F. bidentis, which contains high levels of CA relative to the rates of net CO(2) assimilation, was less than predicted by models of Delta(18)O. Additionally, Delta(18)O was sensitive to small decreases in CA(leaf). However, reduced CA activity in F. bidentis had little effect on net CO(2) assimilation, transpiration rates (E), and stomatal conductance (g(s)) until CA levels were less than 20% of wild type. The values of theta determined from measurements of Delta(18)O and the (18)O isotopic composition of leaf water at the site of evaporation (delta(e)) were low in the wild-type F. bidentis and decreased in transgenic plants with reduced levels of CA activity. Measured values of theta were always significantly lower than the values of theta predicted from in vitro CA activity and gas exchange. The data presented here indicates that CA content in a C(4) leaf may not represent the CA activity associated with the CO(2)-H(2)O oxygen exchange and therefore may not be a good predictor of theta during C(4) photosynthesis. Furthermore, uncertainties in the isotopic composition of water at the site of exchange may also limit the ability to accurately predict theta in C(4) plants.

Carbonic anhydrase isozyme distribution and characterization in metabolic fiber types of the dorsal levator muscle of the blue crab, Callinectes sapidus.

Carbonic anhydrase (CA) distribution and characterization were examined in white and light pink fibers of the dorsal levator muscle of the blue crab. White fibers were structurally and metabolically characterized as fast twitch glycolytic, while the light pink fibers were fast oxidative. All subcellular fractions of both fiber types had significant levels of CA activity; cytoplasmic and microsomal activity was significantly higher in light pink vs white fibers. Cytoplasmic CA from both fiber types was highly sensitive to the inhibitors acetazolamide and chlorzolamide, with Ki values of approximately 2 and 0.4 nM, respectively. Further analysis confirmed that cytoplasmic CA from both fiber types was kinetically similar to the high turnover Type II isoform. It appears that the evolution of the CA Type III isoform, found in vertebrate red muscle, did not occur with the differentiation of metabolic fiber types in crustaceans. Membrane-associated CA, which was also kinetically similar to the Type II isoform, was 20-fold higher in light pink fibers, suggesting a physiological role in facilitated CO2 efflux from the muscle fiber during periods of prolonged maximal activity.

Reduction in carbonic anhydrase activity in the tongue epithelium and submandibular gland in zinc-deficient rats.

We investigated the effects of zinc deficiency on carbonic anhydrase (CA) activity in the tongue epithelium and submandibular gland in rats. Male 4-week-old SD rats were given free access to a diet containing 2.2 (zinc-deficient), 4.1 (low-zinc), or 33.7 (zinc-sufficient) mg zinc/kg diet for 6 weeks. Rats in the fourth group (receiving 33.7 mg zinc/kg) were pair-fed against the zinc-deficient rats. Biochemical analysis at the end of the experimental period indicated that zinc deficiency significantly reduced CA activity in the tongue epithelium and submandibular gland, and the CA activity levels in these tissues seemed to parallel the dietary zinc levels. By enzyme histochemistry, an intensely positive reaction for CA was observed in the middle and basal regions of the taste buds in the circumvallate papilla in the zinc-sufficient and pair-fed (control) rats. The cells in von Ebner's glands also showed a strong positive reaction in control rats, although only a weak reaction product was found in zinc-deficient rats. These results suggest that CA activity is affected by the dietary content of zinc, which is considered to be an indispensable factor for the maintenance of normal taste sensation.

Regulation of carbonic anhydrase expression by zinc, cobalt, and carbon dioxide in the marine diatom Thalassiosira weissflogii.

TWCA1 is the major Zn-requiring isoform of carbonic anhydrase (CA) in the marine diatom Thalassiosira weissflogii. We have examined the roles that trace metals and CO(2) play in the regulation of TWCA1 expression over ranges of concentrations that bracket those encountered in the marine environment. Both steady-state levels of TWCA1 and the kinetics of induction were measured by western analysis. TWCA1 levels correlated well with cellular CA activity levels. TWCA1 was induced at a low CO(2) concentration but the level of induction, as determined by western analysis, was dependent on the availability of Zn. Co effectively substituted for Zn in regulating TWCA1 expression and promoting TWCA1 activity. Upon shift from low to high CO(2), the concentration of TWCA1 decreased. The expression of TWCA1 is diel cycle regulated, and cellular TWCA1 decreased during the dark phase. These results provide the basis for studying the expression of CA in field populations and, taken together with previous radiolabeling studies, provide strong evidence of in vivo metal substitution of Co for Zn in a CA. Our data also support the conclusion that TWCA1 plays a central role in carbon acquisition in T. weissflogii.

Carbonic anhydrase and red blood cell anion exchange in the neotenic aquatic salamander, Necturus maculosus.

Carbonic anhydrase (CA) activity in blood and other tissues and red blood cell (rbc) anion exchange were measured in the mud puppy, Necturus maculosus, in order to gain insight into the strategy for CO2 transport used by these neotenic salamanders and to further explore evolutionary relationships between rbc CA activity and anion exchange in nonmammalian vertebrates. CA activity was detectable in all of the tissues examined, but CA activity in blood was much lower than that in most vertebrates. There was no indication, however, that additional CA had been incorporated into the membrane fraction of other tissues to compensate for this low blood CA activity. In further contrast to most other animals, low levels of CA activity were also detectable in mud puppy plasma. Preliminary characterization of the rbc CA indicated that the Type II, fast-turnover enzyme was indeed present, but that there are a very low number of active sites in mud puppy rbc's. Further experiments showed that the rbc's were highly permeable to anions and that the relative rate of anion flux could be inhibited by 4, 4-diisothiocyanostilbene-2,2-disulphonic acid. Thus, the process of CO2 transport in the blood of mud puppies probably involves components of the Jacobs-Stewart cycle, as in most other vertebrates.

Carbonic anhydrase in deep-sea chemoautotrophic symbioses

Carbonic anhydrase (CA) facilitates the rapid interconversion of carbon dioxide and bicarbonate. It is ubiquitous among organisms, and participates in numerous cellular processes. In several photoautotrophic marine organisms, CA facilitates uptake of inorganic carbon by catalyzing the reversible dehydration of bicarbonate to carbon dioxide, which diffuses more rapidly across cell membranes. In algal/invertebrate symbioses, this mechanism is correlated with significantly elevated CA activity in tissues where zooxanthellae are housed. Here, we determine whether elevated CA activity is also characteristic of tissues involved in inorganic carbon uptake by chemosynthetic invertebrates. Measurements of CA activity in several chemosynthetic clam and vestimentiferan species indicate that CA facilitates inorganic carbon uptake, with high activities present in clam gill tissue, and vestimentiferan plume and trophosome tissues. However levels of CA activity among species varied widely, from very low in mytilids to extraordinarily high in some vesicomyids and vestimentiferans. High CA activity is generally correlated with other adaptations for control of internal chemical environments where symbionts are housed, such as the presence of serum-borne sulfide-binding moieties. These findings suggest that a CA-based mechanism of carbon uptake may be one of a suite of adaptations to provide symbionts with essential metabolites.

Four-Week Safety and Efficacy Study of Dorzolamide, a Novel, Active Topical Carbonic Anhydrase Inhibitor

To investigate the activity and local and systemic safety of the topical carbonic anhydrase inhibitor, dorzolamide hydrochloride. Four-week, double-masked, randomized, placebo-controlled, parallel, three-center study. Referral centers. Forty-eight patients with bilateral open angle glaucoma or ocular hypertension and intraocular pressure (IOP) greater than 22 mm Hg entered the study. Two of 28 patients receiving dorzolamide and two of 20 patients receiving placebo were withdrawn due to adverse experiences. Dorzolamide (2%) or placebo to each eye three times daily for 4 weeks. Diurnal IOP curves; ophthalmologic evaluations including corneal ultrasound pachymetry and endothelial cell count; and systemic evaluations including vital signs, blood chemistries, complete blood cell counts, urinalysis, electrocardiogram, and drug and carbonic anhydrase activity levels in red blood cells. Mean IOP at morning trough (8 AM) decreased from 27.1 mm Hg at baseline to 23.5 mm Hg on day 29 with dorzolamide (-13.3%) compared with a decrease from 27.1 mm Hg to 26.4 mm Hg with placebo (-2.3%). Peak activity occurred 2 hours after administration, with IOP decreasing from 26.8 mm Hg at baseline to 21.8 mm Hg on day 29 with dorzolamide (-18.4%) vs 26.1 mm Hg to 25.5 (-2.4%) with placebo. Mean corneal thickness was slightly increased for the dorzolamide-treated group compared with the placebo-treated group (0.009 mm vs 0.001 mm, respectively, P < .05) and changes in endothelial cell counts were similar (-24 cells/mm2 vs -27 cells/mm2, respectively, P > .25). Mean carbonic anhydrase isoenzyme II activity in red blood cells decreased to 21% of baseline in dorzolamide-treated patients. There were no clinically significant differences in ocular or laboratory parameters between the dorzolamide and placebo groups. Dorzolamide demonstrated significant IOP lowering activity over 4 weeks. It was well tolerated and there were no clinically significant changes in ocular or systemic safety parameters.

Carbonic anhydrase activity in blood of early sheep fetuses

1. 1. The level of carbonic anhydrase activity in the red cells was measured in sheep fetuses at different times after conception: 39, 56, 77, 90 and 140 days, the last being close to full term. Measurements were also made on blood from four of the mothers. 2. 2. There was a low level of the enzyme present in the 39 day fetuses (0.037 enzyme units (E.U.)/100 μg Hb) and its increase up to 90 days of gestation (0.19 E.U./100 μg Hb) had a form approximating exponential. 3. 3. The earliest levels were only 11% of the full term levels and only 4% of the adult levels previously reported. 4. 4. Even the earliest samples were of blood that was fetal rather than embryonic but these results are the earliest carbonic anhydrase activities reported in this mammal.

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.

Light Induction and the Effect of Nitrogen Status upon the Activity of Carbonic Anhydrase in Maize Leaves

The regulation of carbonic anhydrase (CA) activity in maize (Zea mays L.) leaves by light and nitrogen nutrition was determined. CA activity increased by more than 100-fold in illuminated leaves and decreased in leaves placed in the dark; low levels of CA activity were observed in leaves illuminated with low light intensities. CA activity was reduced in plants grown under nitrogen deficiency and recovered only slowly when supplemented with nitrate. Parallel studies were conducted to follow the levels of phosphoenolpyruvate carboxylase. Experiments indicate that the level of CA and phosphoenolpyruvate carboxylase present in leaves may be controlled by similar mechanisms.

Carbonic anhydrase in the normal rat stomach and duodenum and after treatment with omeprazole and ranitidine

A low pH in the lumen of the stomach and duodenum stimulates gastroduodenal mucosal secretion of bicarbonate, particularly in the duodenum. Long-term deprivation of this acid stimulus might affect the ability of the mucosa to secrete bicarbonate, with a consequent decrease in mucosal protection against the acid. This could occur by 'down-regulation' of carbonic anhydrase (CA) activity in the bicarbonate-transporting cells. Levels of CA activity and amounts of CA isoenzymes in rat gastric and duodenal mucosa were determined by biochemical assay and histochemical and immunohistochemical staining. Control animals and animals pre-treated for 4-6 weeks with the histamine H2-receptor antagonist ranitidine (600 mg kg-1 daily) or the H+,K+-ATPase inhibitor omeprazole (28 mg kg-1 daily) were examined. Both drugs are potent inhibitors of gastric secretion of acid. Both gastric and duodenal mucosal total CA activity and the distribution of isoenzymes were very similar in control animals and animals treated with these drugs. In the stomach, CA II was found in the surface epithelial and parietal cells. In the duodenum both CA I and CA II were observed. The staining for CA I was restricted to a small number of villus cells which looked like ordinary duodenal enterocytes. CA II in the duodenum was found in all villus cells, except the goblet cells. The staining decreased gradually from the top to the bottom of the villi and was absent in the crypts. Duodenal bicarbonate secretion is dependent on mucosal CA activity, and the distribution of CA II thus suggests that this alkaline secretion is of villous rather than cryptal origin.