Carbonic anhydrases

Simulation and practical investigation of carbonic anhydrase stability in an industrial solvent system of methyl diethanolamine for carbon dioxide capture

Carbonic anhydrase owing to its potential as an industrial biocatalyst for carbon dioxide sequestration from flue gas has attracted considerable attention in solving global warming problems. A large body of research has been conducted to increase the thermal stability of carbonic anhydrase from different sources against the harsh operational conditions of CO2 capture systems. In contrast to cost-intensive protein engineering methods, solvation with aqueous-organic binary mixtures offers a convenient and economical alternative strategy for retention of protein structure and stability. This study aimed to examine the stabilizing effect of methyl diethanolamine (MDEA) as a component of an aqueous-organic solvent mixture on human carbonic anhydrase II (HCA II) at extreme temperatures. Computational and also spectroscopic examinations were employed for tracking conformational changes and stability evaluation of HCA II in 50:50 (vol %) water: MDEA binary mixture at high temperature. Molecular dynamic (MD) simulation studies predicted the high thermal stability of HCA II in the presence of MDEA. UV absorbance spectra confirmed the thermo-stabilizing effect of the binary solvent mixture on HCA II. While the enzymatic activity of HCA II at 25 °C in the presence of 10, 25, and 50 (vol%) of MDEA was substantially increased, no obvious effect on retention of HCA II activity in the water-MDEA binary solvent mixture at 85 °C was seen. It is shown that the solvation of HCA II in the presence of MDEA could result in the prevention of aggregate formation in high temperatures but not functional stability.Communicated by Ramaswamy H. Sarma.

Studying Sjögren's syndrome in mice: What is the best available model?

Sjögren's syndrome (SS) is a common autoimmune disease characterized by lymphocytic infiltration and destruction of exocrine glands. The disease manifests primarily in the salivary and lacrimal glands, but other organs are also involved, leading to dry mouth, dry eyes, and other extra-glandular manifestations. Studying the disease in humans is entailed with many limitations and restrictions; therefore, the need for a proper mouse model is mandatory. SS mouse models are categorized, depending on the disease emergence into spontaneous or experimentally manipulated models. The usefulness of each mouse model varies depending on the SS features exhibited by that model; each SS model has advanced our understanding of the disease pathogenesis. In this review article, we list all the available murine models which have been used to study SS and we comment on the characteristics exhibited by each mouse model to assist scientists to select the appropriate model for their specific studies. We also recommend a murine strain that is the most relevant to the ideal SS model, based on our experience acquired during previous and current investigations.

The Cellular and Molecular Bases of Allergy, Inflammation and Tissue Fibrosis in Patients with IgG4-related Disease

IgG4-related disease (IgG4-RD) is a spectrum of complex fibroinflammatory disorder with protean manifestations mimicking malignant neoplasms, infectious or non-infectious inflammatory process. The histopathologic features of IgG4-RD include lymphoplasmacytic infiltration, storiform fibrosis and obliterative phlebitis together with increased in situ infiltration of IgG4 bearing-plasma cells which account for more than 40% of all IgG-producing B cells. IgG4-RD can also be diagnosed based on an elevated serum IgG4 level of more than 110 mg/dL (normal < 86.5 mg/mL in adult) in conjunction with protean clinical manifestations in various organs such as pancreato–hepatobiliary inflammation with/without salivary/lacrimal gland enlargement. In the present review, we briefly discuss the role of genetic predisposition, environmental factors and candidate autoantibodies in the pathogenesis of IgG4-RD. Then, we discuss in detail the immunological paradox of IgG4 antibody, the mechanism of modified Th2 response for IgG4 rather than IgE antibody production and the controversial issues in the allergic reactions of IgG4-RD. Finally, we extensively review the implications of different immune-related cells, cytokines/chemokines/growth factors and Toll-like as well as NOD-like receptors in the pathogenesis of tissue fibro-inflammatory reactions. Our proposals for the future investigations and prospective therapeutic strategies for IgG4-RD are shown in the last part.

Intramolecular proton shuttle supports not only catalytic but also noncatalytic function of carbonic anhydrase II

Carbonic anhydrases (CAs) catalyze the reversible hydration of CO(2) to HCO(3)(-) and H(+). The rate-limiting step in this reaction is the shuttle of protons between the catalytic center of the enzyme and the bulk solution. In carbonic anhydrase II (CAII), the fastest and most wide-spread isoform, this H(+) shuttle is facilitated by the side chain of His64, whereas CA isoforms such as carbonic anhydrase III (CAIII), which lack such a shuttle, have only low catalytic activity in vitro. By using heterologous protein expression in Xenopus oocytes, we tested the role of this intramolecular H(+) shuttle on CA activity in an intact cell. The data revealed that CAIII, shown in vitro to have ∼1,000-fold reduced activity as compared with CAII, displays significant catalytic activity in the intact cell. Furthermore, we tested the hypothesis that the H(+) shuttle in CAII itself can facilitate transport activity of the monocarboxylate transporters 1 and 4 (MCT1/4) independent of catalytic activity. Our results show that His64 is essential for the enhancement of lactate transport via MCT1/4, because a mutation of this residue to alanine (CAII-H64A) abolishes the CAII-induced increase in MCT1/4 activity. However, injection of 4-methylimidazole, which acts as an exogenous H(+) donor/acceptor, can restore the ability of CAII-H64A to enhance transport activity of MCT1/4. These findings support the hypothesis that the H(+) shuttle in CAII not only facilitates CAII catalytic activity but also can enhance activity of acid-/base-transporting proteins such as MCT1/4 in a direct, noncatalytic manner, possibly by acting as an "H(+)-collecting antenna."

Decreased total carbonic anhydrase esterase activity and decreased levels of carbonic anhydrase 1 isozyme in erythrocytes of type II diabetic patients

In this exploratory study, we investigated total erythrocyte carbonic anhydrase (CA) estrase activity as well as CA I isozyme concentration in patients with diabetes mellitus type II (DM) and healthy individuals of Howard University Hospital community. Total estrase activity of CA was measured spectrophotometrically using p-nitrophenol acetate before and after inhibition with acetazolamide. CA I isozyme was measured by radial immunodiffusion using monoclonal antibody (CA I) in agarose plates. The study involved 20 consented participants; 10 normal (N) and 10 (DM), 21 to 84 years of age. The study was approved by the Howard University Institution Review Board. The CA activity was measured following lysis of cells as U/min/mL and CA I concentration as mg/l. We observed CA activity as 46.3+/-4(N) and 25+/-2.1 (DM) whereas CA I concentration as 1896+/-125 (N) and 1104 +/-63 (DM). We speculate that the change in the CA activity may of fundamental importance in the regulation of intracellular; pH(i) for the basic control of metabolism in diabetes mellitus. Further, we propose that CA activity is a good candidate for a biomarker of diabetes mellitus for the early detection of insulin resistance because the CA activity variation was proportional to the severity of the diabetes.

Protein expression analysis ofChlamydia pneumoniae persistence by combined surface-enhanced laser desorption ionization time-of-flight mass spectrometry and two-dimensional polyacrylamide gel electrophoresis

The aim of this study was to examine the protein expression profiles of persistentChlamydia pneumoniae by two-dimensional polyacrylamide gel electrophoresis (2D PAGE) and surface-enhanced laser desorption ionization time-of-flight mass spectrometry (SELDI-TOF-MS). Although 2D PAGE is still the method of choice for separating and detecting components of complex protein mixtures, it has several distinct disadvantages; i.e., being labor-intensive and having a bias toward proteins within the dynamic range of the gel condition. Hence, SELDI-TOF-MS technology was used to complement 2D PAGE.C. pneumoniae-infected HEp2 cells were treated with or without IFN-γ, and protein expression profiles were determined at 48 h postinfection (hpi). Unfractionated monolayers were also used for protein profiling by SELDI-TOF, using two different chip surface types: weak cation exchanger and hydrophobic surface. Under IFN-γ-induced persistence,C. pneumoniae expresses an altered protein expression profile. Twenty chlamydial proteins showed differential regulatory patterns by SELDI-TOF-MS, two of which, HSP-70 cofactor, and a hypothetical protein, were identified by 2D PAGE and mass spectrometry. Two additional proteins, phosphatidylserine decarboxylase and 30S ribosomal protein S17, were exclusively identified by SELDI TOF-MS analysis, as these were not present in sufficient quantity for detection by 2D PAGE. We propose that a combination of 2D-PAGE and SELDI-TOF-MS may complement the disadvantages of each technique alone and may provide a rapid and precise screening technique.

Conformational changes and inactivation of bovine carbonic anhydrase II in 2,2,2-Trifluoroethanol solutions

Changes in unfolding and enzymatic activity of bovine carbonic anhydrase II (BCA II) in different concentrations of 2,2,2-trifluoroethanol (TFE) were investigated by 1-anilino-8-naphthalenesulfonate (ANS) fluorescence emission spectra, far-UV CD spectra, and enzyme activity. The results showed that the activity and conformation of BCA II changed according to the concentration of TFE. Significant aggregation was observed when BCA II was denatured at TFE concentrations between 10 and 35% (v/v). When the concentration of TFE exceeded 40%, the aggregation of BCA II was not very obvious. The activity of BCA II decreased almost to zero as the TFE concentration reached 26%. The ANS fluorescence spectra indicated the tertiary conformations of BCA II were more stable in solutions with TFE concentrations lower than 15% (v/v) and higher than 40% (v/v). Far-UV CD spectra showed that high concentrations (higher than 25%) of TFE could induce BCA II to form more alpha-helix structures and caused these structures to be in relatively stable states. The native conformation of BCA II being destroyed after its inactivity indicated that the active sites of BCA II is situated in a limited region and has more flexibility than the whole enzyme molecule.

Molecular determinants of S-glutathionylation of carbonic anhydrase 3

Carbonic anhydrase 3 is easily S-glutathionylated in vivo and in vitro. The protein has two surface-exposed cysteine residues that can be modified. We found that Cys186 is more readily glutathionylated than Cys181. We studied a series of site-specific mutants to identify the residues that interact with Cys186 to make its thiol more reactive. We found that Lys211 is responsible for lowering the pKa of Cys186. We also found that two acidic residues, Asp188 and Glu212, interact with the thiol and actually decrease its reactivity. We speculate that conformational changes that alter the interaction with these three residues provide a mechanistic basis for modulation of the susceptibility of carbonic anhydrase 3 to glutathionylation.

Detection of autoantibody against carbonic anhydrase II in various liver diseases by enzyme-linked immunosorbent assay using appropriate conditions

BACKGROUND

Immunoglobulin G autoantibody against carbonic anhydrase (CA) II has been detected in the sera of patients with a variety of autoimmune diseases. Antibody against CAII has also been described as a serological marker for distinguishing between cases of autoimmune cholangitis (AIC) and those of primary biliary cirrhosis (PBC). However, the optimal antibody measurement conditions (enzyme-linked immunosorbent assay: ELISA) have not yet been established. Moreover, we also found that a small amount of an IgG-like material exists in purchased CAII reagents, which causes pseudopositive reactions.

METHODS

The sera of 96 patients with liver disease were examined for the presence of anti-CAII antibody using antigen (CAII) not containing the IgG-like material as the most suitable measurement conditions. Compared with the anti-CAII antibody prevalence of 3.8% found in normal subjects, a significantly higher seroprevalence of the antibody was detected in patients with PBC (31.0%, P<0.02), autoimmune hepatitis (AIH) (50.0%, P<0.01) and chronic viral hepatitis (27.5%, P<0.01). But, in cases of PBC, no significant correlation was noted between the level of anti-CAII antibody and the presence of anti-mitochondrial antibodies (AMA).

CONCLUSIONS

While CAII may be a target antigen in autoimmune diseases, the anti-CAII antibody is not likely to be a specific marker of AIC. The optimum measurement conditions for the ELISA for anti-CAII antibody would provide us with valuable information to elucidate the underlying immunological abnormalities in liver diseases.

Measurement of Erythrocyte Carbonic Anhydrase Isozymes (CA-I and CA-II) in Racehorses and Riding Horses

Equine carbonic anhydrase isozymes (CA-I and CA-II) were purified from erythrocytes by several column chromatography. Polyclonal anti-CA-I and anti-CA-II sera were produced in rabbits. Sensitive competitive enzyme-linked immunosorbent assays (ELISA) were established to determine the developmental changes in CA-I and CA-II levels in equine erythrocytes. Concentrations of CA-I and CA-II in erythrocytes from 150 clinically normal thoroughbreds (123 racehorses and 27 riding horses) were determined by ELISA. Mean (+/- SD) concentrations of CA-I and CA-II in racehorses were 1.70 +/- 0.48 and 0.94 +/- 0.13 mg/g hemoglobin (Hb), respectively. Mean concentrations of CA-I and CA-II in riding horses were 2.34 +/- 0.52 and 0.76 +/- 0.08 mg/g Hb, respectively. When the CA levels in racehorses and riding horses were compared, the CA-I level in riding horses was higher than that in racehorses (p=0.01). The CA-II level in racehorses was higher than that in riding horses (p=0.02). These data suggest that the levels of CA isozymes in erythrocytes of racehorses were influenced by chronic physical stress. The CA-I concentration in erythrocytes of 2-month-old horses was approximately 0.25 mg/g Hb. The CA-I level noticeably increased during the first year of life and approached normal adult levels by 2 years. The CA-II level decreased slightly with age, indicating different regulation of CA-I and CA-II expression during development.

Colon cancer: prevalence, screening, gene expression and mutation, and risk factors and assessment

Colon cancer detection at an early stage and identifying susceptible individuals can result in reduced mortality from this prevalent cancer. Genetic events leading to the development of this cancer involve a multistage progression of adenoma polyps to invasive metastatic carcinomas. Currently, there is no satisfactory screening method that is highly specific, sensitive, or reliable. Dietary patterns associated with the greatest increase in colon cancer risk are the ones that typify a diet rich in fat and calories, and low in vegetable, fruits, and fibers. Genetic susceptibility to environmental carcinogenesis must be factored into the risk assessment for this cancer. Many genes have been shown to be associated with increased expression and mutations in colorectal cancer patients. These genes have been reviewed; it is hoped that by carefully selecting a number of them, a molecular approach that is suitable for arriving at a tumorigenic expression index is developed, which will reliably detect this cancer at an early stage (i.e., before it metastasizes), especially in exfoliated samples (e.g., stool and blood), so that appropriate intervention strategies can be implemented. Illustrated herein is the utility of employing real-time reverse transcriptase polymerase chain reaction (RT-PCR) to quantitatively measure gene expression, and develop an index that is specific for this cancer, which if perfected may result in a reliable and sensitive screening technique for colorectal cancer detection.

Expression and localization of carbonic anhydrase in bovine mammary gland and secretion in milk

Little attention has been paid to carbonic anhydrase VI (CA VI), a secretory type isozyme, in the bovine mammary gland, although the gland is an important exocrine gland and CA VI is known to localize in exocrine glands such as salivary and lacrimal glands in various animal species. In the present study mRNA expression and protein localization of CA VI in isolated gland tissues and in cloned epithelial cells from the mammary gland of Holstein cows (Bos taurus) were observed by reverse transcript polymerase chain reaction and immunocytochemistry. Also, changes of CA VI concentrations in milk were measured for 2 months postpartum by an enzyme-linked immunosorbent assay. CA VI gene expression was detected in the gland tissues and epithelial cells, and CA VI protein was localized in the cytoplasm of the epithelial cells. Colostrum contained the highest concentration of CA VI protein (100 ng/ml), decreasing in an exponential manner (P<0.001). We conclude that bovine mammary epithelial cells synthesize and secrete CA VI in colostrum at higher concentration than in normal milk, implying its role to compensate for low CA VI secretion in neonatal calves.

Carbonic anhydrase from bovine bone

In this research, carbonic anhydrase enzyme, which was taken from the bones of an animal, was purified and characterized for the first time. For this, the bones of a young cow were used. The purification treatment was completed in three steps. Three different isoenzymes, such as peripheral, cystolic, and integral from the bone-cell cytozolic isoenzyme were purified and characterized. In purification of the three isoenzymes, the technique of affinity chromatography, which utilized Sepharose-4B-L-Tyrosine-Sulphanylamide, was used. In measuring the activities of enzymes, two different methods were applied. These are the esterase methods that utilize hydratase and p-nitrophenylacetate as substrate. The measurement of proteins was done with the methods of Bradford and Coomassie Brillant Blue. The optimum pH and temperature of each enzyme were measured and molecular weights were measured by gel-filtration. Its purity was examined by SDS-PAGE (3-10% alternating) electrophoresis and the inferior unit was defined. The inhibition effects of some chemicals were tested for each of the three isoenzymes.

Müller cell differentiation in the zebrafish neural retina: evidence of distinct early and late stages in cell maturation

The vertebrate neural retina is mainly composed of cells of neuroectodermal origin. The primary cell types found in all vertebrate retinas are several categories of neurons and the archetypical retina glial cell the Müller cell. Although the neurons and the single glial cell type of the retina are specialized for very distinct functions, they all have a common developmental origin within the tissue. How the distinctions between cell types, in particular between neurons and glia, arise during embryonic development remains a central issue in neurobiology. In this report, we examine the genesis of Müller glial cells during zebrafish (Danio rerio) eye development. Particular emphasis is placed on the expression of the Müller cell maturation markers carbonic anhydrase and glutamine synthetase. In addition, we report that the HNK-1 monoclonal antibody, which identifies a particular glycoconjugate frequently found on cell surface recognition molecules, also identifies zebrafish retina Müller cells early in development. The expression patterns of these three markers clearly show that the Müller cells mature in stages: HNK-1 labeling and glutamine synthetase arise earlier than carbonic anhydrase expression. In addition, the embryonic zebrafish neural retina is characterized by the presence of amoeboid, carbonic anhydrase-positive microglial cells even before the genesis of retinal neuroectodermal glia. The stepwise maturation of the glia is likely to be indicative of an overall retinal maturational program in which cell differentiation and the expression of certain phenotype-defining gene products may be separately regulated.

Crystal structure of S-glutathiolated carbonic anhydrase III

S-Glutathiolation of carbonic anhydrase III (CAIII) occurs rapidly in hepatocytes under oxidative stress. The crystal structure of the S-glutathiolated CAIII from rat liver reveals covalent adducts on cysteines 183 and 188. Electrostatic charge and steric contacts at each modification site inversely correlate with the relative rates of reactivity of these cysteines toward glutathione (GSH). Diffuse electron density associated with the GSH adducts suggests a lack of preferred bonding interactions between CAIII and the glutathionyl moieties. Hence, the GSH adducts are available for binding by a protein capable of reducing this mixed disulfide. These properties are consistent with the participation of CAIII in the protection/recovery from the damaging effects of oxidative agents.

Distribution of carbonic anhydrase isozyme VI in the developing bovine parotid gland

The distribution of bovine carbonic anhydrase isozyme VI (CA-VI), purified from bovine saliva, was studied immunohistochemically using antiserum against bovine CA-VI in bovine parotid glands during fetal and postnatal development. A weak expression of CA-VI in undifferentiated epithelial cells and ductal cells was observed in a 4- to 5-month-old fetus with a 26-cm crown-rump length. The reaction in both acinar and ductal cells subsequently persisted during late gestation and birth. Although anti-CA-VI reactivity was still seen in both regions immediately following birth, the reactivity had almost completely disappeared from most duct segments by 1 month following birth. Changes in the localization and time-dependent expression of the isozyme in parotid glands may reflect changes in the biological function of structurally closely related isozymes.

Isolation and measurement of carbonic anhydrase isoenzymes in erythrocytes of dogs

OBJECTIVE

To purify canine carbonic anhydrase (CA) isoenzymes CA-I and CA-II and to determine concentrations of CA-I and CA-II in erythrocytes of Beagles and dogs native to Japan.

SAMPLE POPULATION

Blood samples from 116 Beagles, including 24 pregnant Beagles, and blood samples from 29 dogs native to Japan.

PROCEDURE

Canine CA-I and CA-II were purified by use of column chromatography. Concentrations of CA-I and CA-II in erythrocytes of dogs were determined, using an ELISA.

RESULTS

Mean (+/- SD) concentrations of CA-I and CA-II in erythrocytes of Beagles were 3.21+/-0.86 and 1.63+/-0.39 mg/g of Hb, respectively. Mean concentration of CA-I was greater in male Beagles than female Beagles. In contrast, mean concentration of CA-II was greater in female Beagles than male Beagles. Furthermore, concentration of CA-II was greater in pregnant female Beagles than male or nonpregnant female Beagles. Mean concentrations of CA-I and CA-II in erythrocytes of dogs native to Japan were 11.03+/-4.39 and 3.29+/-0.91 mg/g of Hb, respectively. Mean concentration of CA-I was greater in male dogs from Japan than female dogs from Japan.

CONCLUSIONS AND CLINICAL RELEVANCE

The ELISA used in this study proved to be precise and sensitive for determining CA-I and CA-II concentrations in dogs. The ELISA may enable study of changes in isoenzymes associated with hereditary or metabolic disorders of blood or other body fluids, using only a small sample. Measurement of the concentrations of CA isoenzymes in dogs may be of diagnostic value.

Characteristics of myoglobin, carbonic anhydrase III and the myoglobin/carbonic anhydrase III ratio in trauma, exercise, and myocardial infarction patients

Carbonic anhydrase III (CA III) is an enzyme present in skeletal muscle which is released into circulation following injury. Myoglobin (Mb) is a heme protein located in skeletal, smooth, and cardiac muscle which is also released after injury. Because CA III is not present in myocardium, combining serum CA III and Mb measurements may improve the specificity of Mb as an early diagnostic marker for myocardial infarction (MI) provided that a fixed ratio of Mb and CA III is released from skeletal muscle following cell injury. We examined release of Mb and CA III for exercise subjects (n=12), trauma patients (n=18), and MI patients (n=10) following emergency department admission. A fixed ratio of Mb/CA III had medians of 3.505 (range: 1.05-6.76) and 2.890 (range: 0.97-3.97) for exercise and trauma subjects, respectively, in samples collected within 5 h of the event. The Mb/CA III ratio was significantly higher (P<0.001) in MI patients (median: 35.395; range: 8.65-170.45) during this same time. This study confirmed that Mb and CA III are released in a fixed ratio following exercise, showed no significant difference in the ratio for trauma patients, and demonstrated significant ratio elevation for MI patients. These data suggest the ratio to be a useful diagnostic indicator of MI.

Purification and characterization of carbonic anhydrase from bovine erythrocyte plasma membrane

Carbonic anhydrase (CA) was purified from bovine erythrocyte plasma membrane and characterized in this study. For this purpose, the blood taken from young animals was hemolysed, the membrane fraction was separated, and this fraction was repeatedly washed. The enzyme (CA) was removed from the membrane with buffered TritonX-100 (1%); it could be purified at a factor of 22.8 by affinity chromatography. The CA obtained from erythrocyte membrane has an esterase activity as well as hydratase activity. The Vmax and Km of the enzyme for the substrate (p-nitrophenyl acetate) are 1.948x10(-3) mM/L x dak, and 3.596 mM, respectively. The purification degree of the enzyme was controlled by SDS-PAGE (3-10), which showed two distinct bands. It was determined that the enzyme had activity within the pH range of 4.5-9.5 and that the optimal pH was 7.5. The temperature at which it showed activity was 20-60 degrees C and optimal temperature was 37 degrees C. Molecular weight of CA was found to be 29844 and 61706 Dalton by gel filtration. On the other hand, sulfanilamide and acetazolamide affected the enzyme.

Localization of carbonic anhydrase in guinea pig Bowman's glands

We examined the histochemical localization of carbonic anhydrase (CA) in Bowman's glands by light and electron microscopy. Neither CAI nor CAII was detected immunohistochemically in the duct cells. However, by enzyme histochemistry the duct cells revealed electron-dense precipitates demonstrative of CA in the microvilli and intercellular digitations. The reaction product was also noted in small vesicles in the cytoplasm of duct cells. In cells of the acini, the well-developed short microvilli, basolateral cell membrane, and mitochondria along the basolateral membrane showed strong deposits indicating CA activity. Dense reaction product of CA was also detected in a small core within the electron-lucent granules of the secretory cells, although CAI and CAII were not detected by immunostaining in the secretory granules. Although the functional significance of CA in Bowman's glands is obscure, the enzyme may play a role in regulation of pH and ion balance in the mucous layer covering the olfactory epithelium. The presence of CA activity in the ducts suggests that these structures are not simple tubes serving as a conduit for secretory substances but participate in modifying the luminal content by secreting CA. (J Histochem Cytochem 47:1525-1531, 1999)

Gly-63-->Gln substitution adjacent to His-64 in rodent carbonic anhydrase IVs largely explains their reduced activity

Carbonic anhydrase (CA) IV is a glycosyl-phosphatidylinositol-anchored isozyme expressed on plasma membranes of capillary endothelial cells and certain epithelial cells of the nephron, the colon, and the genitourinary tract. CA IVs purified from bovine and rabbit lungs are high-activity enzymes, like human CA IV, while CA IV from mouse and rat lungs had only 10-20% as much catalytic activity. To explain the molecular basis for these differences in activity, we isolated and characterized the full-length cDNAs for bovine and rabbit CA IVs and compared their sequences to those we previously reported for human, murine, and rat CA IVs. These comparisons led us to postulate that a Gly-63-->Gln substitution adjacent to His-64 in the rodent enzymes accounts for their lower activity. To test this hypothesis, we made the Gly-63-->Gln mutants of bovine and rabbit CA IVs and the Gln-63-->Gly mutant of murine CA IV by site-directed mutagenesis, and compared the activities of mutant and wild-type CA IVs expressed in COS-7 cells. In addition, we produced recombinant cDNAs expressing secretory forms of the Gly-63 and Gln-63 forms of each of the three enzymes and compared the activities of the enzymes purified from transfected COS-7 cell secretions with the activities of CA IVs purified from lungs. These studies demonstrated that Gly-63 is important for the high activity of bovine and rabbit CA IVs, and they showed that the low activity of murine CA IV could be improved by the Gln-63-->Gly substitution. We suggest that the lower activity of the rodent CA IVs can be largely explained by the Gln-63 substitution which reduces the efficiency of proton transfer by the adjacent His-64.

Effect of testosterone on carbonic anhydrase and MG(2+)-dependent HCO3-stimulated ATPase activities in rat kidney: comparison with estradiol effect

Effects of testosterone administration (TP; 1-3 mg/kg body weight, S.C., once daily for 7 days) on the cytosol carbonic anhydrase (CA) and tubular brush border Mg(2+)-dependent HCO3(-)-stimulated ATPase (Mg(2+)-HCO3(-)-ATPase) activities of normal and castrated male and female rat kidney were compared with estradiol (E2) effects. TP decreased kidney CA activity in a dose-dependent manner in all four animal conditions, and negative correlations were observed between cytosol CA activity and serum testosterone concentration. However, brush border Mg(2+)-HCO3(-)-ATPase activity was not affected by testosterone. Orchiectomy increased only CA activity and its value recovered to normal levels by 3 mg/kg TP replacement, whereas Mg(2+)-HCO3(-)-ATPase activity did not change. In the previous study, on the other hand, E2 administration activated both kidney enzymes in normal male rats and only Mg(2+)-HCO3(-)-ATPase in normal female rats. Testosterone and E2 conversely affected kidney CA activity in male rats. These facts suggest that the cytosol CA may control kidney functions on H+ and HCO3- metabolism under the balance of both sex hormones in the living body.

Molecular cloning of the mouse gene coding for carbonic anhydrase IV

Carbonic anhydrase IV (CA IV) is expressed on apical surfaces of renal tubular epithelium and endothelium of specialized capillary beds. It plays a key role in bicarbonate reabsorption in kidney and in CO2 transport in other tissues. The human cDNA and genomic sequences have been cloned and characterized. Here we report the cloning and characterization of the entire mouse CA IV gene (contained in two overlapping lambda clones), which should enable generation of targeting constructs for disrupting the mouse CA IV gene to produce mouse models for in vivo analysis of CA IV gene function. The gene is approximately 8.2 kb long and contains eight exons ranging from 54 to 434 bp in length. The first exon (exon 1a) encodes the signal sequence. Exons 1b through 7 encode the remaining coding sequences. Exon 7 encodes the C terminus of the membrane-associated protein, as well as the 242-bp 3' untranslated sequence. The nucleotide sequence alignment between mouse and rat CA IV cDNAs reveals 84% identity. The nucleotide sequence alignment between mouse and human CA IV shows 69% identity in the coding region and all of the exon-intron boundaries are conserved, as are the sizes of the introns. The corresponding mouse and human exons are similar, except for the length of the untranslated regions in exons 1a and 7 and two small insertion/deletion events in exons 1a and 4. The 5' flanking region of the mouse gene (-300 to -1) is GC rich and contains 16 CpG dinucleotides. A TATA box sequence and several transcription factor binding sequences are identified upstream of exon 1a. Comparison of the nucleotide sequences surrounding the TATA box (-300 to -1) between mouse and human CA IV genes revealed 70% identity, indicating that regulatory sequences are as highly conserved as coding sequences between mouse and human CA IV genes.

Carbonic anhydrase IV expression in rat and human gastrointestinal tract regional, cellular, and subcellular localization

Carbonic anhydrase IV (CA IV) is a glycosylphosphatidylinositol-linked isozyme previously identified on the surface of renal tubular epithelium and certain populations of vascular endothelium. This report identifies the regional, cellular, and subcellular localization of CA IV in the rat gut. Northern blot and RT-PCR analyses demonstrated little CA IV expression in stomach or proximal small intestine, but abundant expression in distal small and large intestine. In contrast, CA II mRNA was abundant in stomach, decreased in proximal small intestine, low in distal small intestine, and abundant in large intestine. CA I mRNA was detected only in large intestine. The regional distribution of CA IV activity correlated with distribution of CA IV mRNA. Immunohistochemistry localized CA IV to the apical plasma membrane of the mucosal epithelium in distal small intestine and large intestine. Signal intensity was greatest in colon. CA IV was additionally found in submucosal capillary endothelium of all gastrointestinal regions. Immunohistochemical findings in human stomach and colon paralleled those in the rat. These studies demonstrate pre-translational isozyme-specific regulation of CA expression along the cranial-caudal axis of the gastrointestinal tract. The regional, cellular, and subcellular localizations are consistent with participation of CA IV in the extensive ion and fluid transport in the distal small and large intestine.

Carbonic anhydrase IV: role of removal of C-terminal domain in glycosylphosphatidylinositol anchoring and realization of enzyme activity

Carbonic anhydrase IV (CA IV) is a glycosylphosphatidylinositol (GPI)-anchored membrane protein expressed on the plasma membrane of specific epithelial and endothelial cells. The human cDNA encodes a 312-amino-acid precursor which includes an NH2-terminal signal sequence (residues -18 to -1) that is removed and a C-terminal hydrophobic domain which is cleaved to permit transfer to the GPI anchor. Using biochemical methods, we established that Ser266 is the site of attachment of the GPI anchor to CA IV from human lung. Based on this result, we constructed missense mutants S266F and G267F and a truncation mutant, G267X, and investigated the role of removal of the C-terminal hydrophobic domain on the synthesis and processing of CA IV in transfected COS cells. The G267F mutation had no effect on CA IV expression. By contrast, the S266F mutation prevented removal of the C-terminal domain and the S266F CA IV was inactive, not GPI-anchored, and not expressed on the cell surface. The G267X C-terminal deletion mutation resulted in secretion of an amount of CA IV severalfold higher than the amounts found in cells transfected with wild type cDNA. These results demonstrate that removal of the C-terminal hydrophobic domain is necessary both for GPI anchoring and for realization of CA IV activity. They further show that bypassing C-terminal processing by deletion of the hydrophobic domain leads to secretion of a fully active CA IV in amounts far greater than those which accumulate in cells expressing the wild type, GPI-anchored CA IV.

Mitochondrial carbonic anhydrase (isozyme V) in mouse and rat: cDNA cloning, expression, subcellular localization, processing, and tissue distribution

When the human cDNA, isolated on the basis of homology to the murine carbonic anhydrase (CA) "Y" was expressed in COS cells, the human CA was targeted to and processed in mitochondria, as expected for CA-V. However, tissue distribution reported for the corresponding mouse CA Y mRNA was much more limited than that reported for the distribution of CA-V immunostaining in rat tissues. To determine whether the murine cDNA actually encodes a mitochondrial CA activity and to compare the tissue distribution of the homologous murine and rat gene products, we used reverse transcription-PCR to reisolate the murine CA-V candidate cDNA and used the murine cDNA probe to isolate the homologous rat cDNA. We compared the two cDNA sequences, the activities they expressed after transfection of COS cells, and the sites of N-terminal processing of expressed products. In addition, we used antibodies to the C-terminal peptides predicted from each cDNA to compare distribution of CA-V in mouse and rat tissues and to identify CA-Vs in mitochondria isolated from mouse and rat liver. From these studies, we conclude that both mouse and rat CA-V candidate cDNAs encode active CAs that are targeted to and processed in mitochondria and that there are real differences in tissue distribution of CA-V between mouse and rat. However, the findings that are M(r) of CA-V in rat tissues is smaller than that previously reported and that the tissue distribution also differs lead us to conclude that the antibody used in prior reports most likely misidentified another antigen in rat tissues as CA-V.

A novel carbonic anhydrase II mRNA isolated from mature chicken testis displays a TATA box and other promoter sequences in a leader 5' untranslated region not present in somatic tissues

The primary structure of a novel carbonic anhydrase II-encoding cDNA clone (CAII) isolated from a chicken testis cDNA library is presented. The size of the CAII mRNA obtained from meiotic and haploid chicken testis cells is larger than the corresponding mRNA from immature testis and somatic tissues. The nucleotide sequence of the chicken testis CAII clone revealed a protein-coding region identical to the published sequence of CAII mRNA from erythroid cells. However, the 5' untranslated region (UTR) of the testis CAII mRNA is larger than the corresponding somatic sequence. The 5' UTR contains a leader sequence not present in the CAII mRNA isolated from erythroid cells or chick retina. The additional 5' UTR of the mRNA displays a TATA box, located 23-30 bp upstream from the cap site of the CAII mRNA transcribed in erythroid cells, and several G+C-rich boxes. Our results suggest that the use of a testis-specific promoter would result in the incorporation of somatic promoter sequences into the 5' UTR of the testis message.

Expression of carbonic anhydrase isozymes II and III in developing bovine parotid gland

Two cytosolic carbonic anhydrase isozymes (CA-II and CA-III) were studied by immunohistochemistry in bovine parotid glands during fetal development. In a 3-month-old fetus of crown-rump length (CRL) 17 cm, the expression of CA-II in undifferentiated epithelial cells was observed, whereas immunostaining for CA-III remained negative. At 26 cm CRL (4-5 months old), weak expression of CA-III in large ductal epithelial cells was noted. The accumulation of secreted granules in primary acinar cells was initially observed at this stage. In a newborn calf, anti-CA-II reactivity almost disappeared from most duct segments. The time-dependent expression and distribution of the isozymes in parotid glands may reflect different biological functions of these structurally closely related isozymes. Bovine parotid acinar cells of fetuses would thus appear to possess all the cellular structures and immunohistochemical properties at 4 and 5 months of gestation. CA-II subsequently disappeared from duct segments and nearly all acinar cells in adults were present at or just after birth.

Human mitochondrial carbonic anhydrase: cDNA cloning, expression, subcellular localization, and mapping to chromosome 16

A full-length cDNA clone encoding human mitochondrial carbonic anhydrase (CA), CA V, was isolated from a human liver cDNA library. The 1123-bp cDNA includes a 55-bp 5' untranslated region, a 915-bp open reading frame, and a 153-bp 3' untranslated region. Expression of the cDNA in COS cells produced active enzyme. The 34-kDa precursor and 30-kDa mature form of CA V were identified on Western blots of COS-cell homogenates by a CA V-specific antibody raised to a synthetic peptide corresponding to the C-terminal 17 aa of CA V. Both 34-kDa and 30-kDa bands were also present in mitochondria isolated from transfected COS cells, whereas only the 30-kDa band was present in mitochondria isolated from normal human liver. The N-terminal sequence determined directly on the 30-kDa soluble CA purified from transfected COS cells indicated that processing of the precursor to mature human CA V involves removal of a 38-aa mitochondrial leader sequence. The 267-aa sequence deduced for mature human CA V shows 30-49% similarity to amino acid sequences of previously characterized human CAs (CA I-CA VII) and 76% similarity to the corresponding amino acid sequence deduced from the mouse cDNA. PCR analysis of DNAs from human-rodent somatic cell hybrids localized the gene for CA V to human chromosome 16, the same chromosome to which CA VII has previously been mapped.

Differential expression of carbonic anhydrase isozymes in microglial cell types

Microglia cells have been shown to express carbonic anhydrase. Using carbonic anhydrase histochemistry and immunohistochemistry, different types of central nervous system microglial cells were detected, which expressed two main carbonic anhydrase (CA) isozymes during the early postnatal stage of development and after peripheral nerve injury in the spinal cord of adult rats. Amoeboid and reactive microglial cells were heavily immunostained for CA-II and CA-III and showed colocalization with complement receptor type 3 and Griffonia Simplicifolia B4 isolectin. Resting microglial cells in the brain and spinal cord showed faint CA-III staining and were negative for CA-II. These results show that not only CA-II, but also CA-III isozyme is represented in the central nervous system and carbonic anhydrase activity may correlate with metabolic and immunological changes of microglial cells. These data also further strengthen the idea of the mesodermal origin of central nervous system macrophages.

Comparative immunohistolocalization of carbonic anhydrase isozymes I, II and III in the equine and bovine digestive tract

Immunohistochemical localizations of carbonic anhydrase isozymes (CA-I, CA-II and CA-III) in equine and bovine digestive tracts were studied. In the horse, epithelial cells in both the oesophagus and non-glandular part of the stomach lacked all three isozymes. In contrast, surface epithelial and parietal cells in the glandular region of the stomach showed reactivity for CA-II. In the small intestine, absorptive columnar cells covering the villi in the duodenum were positive for CA-II. The epithelium of the jejunum and ileum lacked all three isozymes. In the large intestine, CA-II was detected in the columnar cells in the upper part of the crypt. In cattle, epithelial cells of the oesophagus showed reactions for CA-I and CA-III but not for CA-II. Although the absorptive epithelial cells of the small intestine lacked CA-I, CA-II and CA-III, those of the upper part of large intestine crypts were heavily stained for all three isozymes.

Simultaneous measurement of intracellular and extracellular carbonic anhydrase activity in intact muscle fibres

The presence and properties of membrane-bound carbonic anhydrases have been difficult to establish with conventional enzymological and immunohistochemical techniques. We have therefore studied carbonic anhydrase (CA) activity in single intact crayfish muscle fibres by superfusing them alternately with a 4-(2-hydroxyethyl)-1-piperazine-ethanesulphonic acid (HEPES)-buffered and a 5% CO2/HCO3(-)-buffered solution (pH of both solutions 7.4) while recording the intracellular pH (pHi) and extracellular surface pH (pHs) with H(+)-selective microelectrodes. In order to prevent regulation of pHi, Na+ ions were replaced with N-methyl-D-glucamine. Application of the CO2-containing solution produced a fast fall in pHi coupled with a marked (0.5-0.8 pH units) transient increase in pHs. Submicromolar concentrations of acetazolamide (AA) and benzolamide (BA) immediately blocked the pHs transients. A concentration of 8 x 10(-8) M (both compounds) reduced the response by 50%. A more prolonged application of BA and AA at concentrations of 10(-7) M and higher slowed the CO2-induced fall in pHi, which attained a rate corresponding to uncatalysed intracellular CO2 hydration at an AA concentration of 10(-4) M. The effect of BA and AA on the pHi changes developed with a time constant of 25 +/- 4 min and 7.6 +/- 1.5 min respectively, indicating that BA is less permeant than AA. CNO- ions (5 x 10(-4) M) had little effect on the CO2-induced pHs and pHi changes.(ABSTRACT TRUNCATED AT 250 WORDS)

Human carbonic anhydrase IV: cDNA cloning, sequence comparison, and expression in COS cell membranes

We have isolated a full-length cDNA for human carbonic anhydrase IV (CA IV) from a lambda gt10 human kidney cDNA library. The 1105-base-pair (bp) cDNA contains a 47-bp 5' untranslated region, a 936-bp open reading frame, and a 122-bp 3' untranslated region. The deduced amino acid sequence is colinear with the N-terminal sequence and the sequence of several tryptic peptides of human lung CA IV. It includes an 18-amino acid signal sequence, a 260-amino acid region that shows 30-36% similarity with the 29-kDa cytoplasmic CAs (CA I, CA II, and CA III), and an additional 27-amino acid C-terminal sequence that ends in a 21-amino acid hydrophobic domain. Of the 17 "active site" residues that are highly conserved in other human CAs, 16 are also present in CA IV. Expression of the cDNA in COS cells produced a 35-kDa enzyme that was membrane associated, resistant to inactivation by SDS, contained no carbohydrate, and reacted on Western blots with antiserum to the 35-kDa CA IV from human lung. Treatment of membranes from transfected COS cells with phosphatidylinositol-specific phospholipase C released 20-30% of the expressed enzyme from membranes, indicating that at least 20-30% of the expressed enzyme was anchored to membranes by a glycosyl-phosphatidylinositol linkage.

The effect of bile salts on carbonic anhydrase

Bile salts are potent inhibitors of bovine carbonic anhydrase and human carbonic anhydrase I and human carbonic anhydrase II. To further characterize the binding of bile salts to carbonic anhydrase, rate constants for the CO2 hydration reaction in the presence of deoxycholate, cholate, glycocholate and taurocholate were determined using stop-flow experiments. Values for the Michaelis-Menton dissociation constant for bovine carbonic anhydrase, human carbonic anhydrase I and human carbonic anhydrase II were found to be 5.2, 9.2 and 13.2 mmol/L, respectively. The inhibition constant values for the various bile salts tested ranged from 0.1 to 1 mmol/L for bovine carbonic anhydrase, 1.6 to 2.4 mmol/L for human carbonic anhydrase I and 0.09 to 0.7 mmol/L for human carbonic anhydrase II. Our results suggest a mechanism of noncompetitive carbonic anhydrase inhibition for bile salts. Bile-salt binding to carbonic anhydrases as measured by scanning molecular sieve chromatography resulted in an increase in partition radius, molecular volume and surface area. The partition radius increased from 24 A to 28 A in the presence of 2.5 mmol/L sodium deoxycholate at critical micelle concentration. As determined by sedimentation equilibrium measurements, approximately 1 gm of carbonic anhydrase will bind 0.03 gm of deoxycholate, suggesting three to six binding sites for bile salt on the carbonic anhydrase molecule. The conformational changes and inhibition of carbonic anhydrases resulting from bile-salt binding may be important to the regulation of enzymatic activity in tissues along the enterohepatic circulation; by limiting bicarbonate availability this interaction may also contribute to the metabolic derangements seen in patients with cholestatic liver disease.

Antibodies to carbonic anhydrase in systemic lupus erythematosus and other rheumatic diseases

OBJECTIVE

Autoantibodies to CA were demonstrated in the sera of patients with systemic lupus erythematosus (SLE) and some other rheumatic diseases. This study was undertaken to define the isoform and species specificity of these reactions, as well as to develop a method for detecting immune complexes.

METHODS

Antibodies to CA were sought by enzyme-linked immunosorbent assay (ELISA) and by Western immunoblotting.

RESULTS

An increased prevalence of CA autoantibodies was detected, by both methods, in patients with SLE, scleroderma, and polymyositis, compared with controls. In SLE patients, CA autoantibodies occurred preferentially in those with anti-U1 RNP or anti-U1 RNP and Ro/SS-A. Some sera reacted with only the CA I or CA II isoform, while approximately 50% of sera that were CA positive reacted with both isoforms. The autoantibodies reacted preferentially with the human enzymes, rather than the bovine CA, both on Western blot and by ELISA: Selected IgG F(ab')2 fragments from anti-CA-containing sera specifically inhibited the enzyme activity of CA, and the CA inhibitor acetazolamide partially inhibited the binding of anti-CA to CA. Thus, at least a part of autoanti-CA is directed toward the active site of CA. Finally, CA molecules were detected as immune complexes in sera from selected anti-CA-positive patients.

CONCLUSION

Autoantibodies to CA represent a previously unrecognized autoantibody to an abundant intracellular protein of the human erythrocyte.

Nucleotide sequence of a cDNA encoding rat brain carbonic anhydrase II and its deduced amino acid sequence

A carbonic anhydrase II (CAII)-encoding cDNA clone was isolated from a rat brain lambda gt11 library. The 1459-bp cDNA codes for 260 amino acids with sequence similarity to mouse and human CAII and hybridizes to a single 1.7-kb mRNA.

Thermal denaturation of erythrocyte carbonic anhydrase

An experimental study on the thermal behaviour of erythrocyte carbonic anhydrase was carried out with the main aim to estimate the thermodynamic parameters that control the stability of the enzyme. The effects of thermal denaturation on the catalytic properties of the enzyme were also investigated. Below 60 degrees C the enzyme was found to be very stable, whereas between 60 and 65 degrees C a drastic decrease in the biological activity was observed. From the obtained results some considerations were made about the stabilization of the active form of the protein.

Induction of carbonic anhydrase I isozyme precedes the globin synthesis during erythropoiesis in K562 cells

Induction of carbonic anhydrase isozyme I (CA-I) by erythropoietin or hemin was investigated using erythroleukemia (K562) cells. Immunological estimation and purification of carbonic anhydrases showed that untreated K562 cells contained only carbonic anhydrase isozyme II(CA-II), while incubation of the cells with 2 units of erythropoietin (EP) per ml of the incubation medium or with 50 microM hemin resulted in the induction of CA-I. The purified CA-I induced in K562 cells was enzymatically and immunologically identical to that from mature erythrocytes. Flow cytometric analysis showed that incubation of K562 cells with EP as well as hemin induced CA-I at the 3rd h, while alpha-globin was detected at the 8th h. Northern blot analysis of CA-I mRNA using a cloned genomic DNA as a probe showed that mRNA of CA-I was induced by EP. These results suggest that induction of CA-I is regulated at the transcriptional level during developmental changes of erythroid cells, and that CA-I may play a physiologically important role during erythroid differentiation.

Sexual difference and organ specificity of the effect of estradiol on carbonic anhydrase and Mg(2+)-HCO3(-)-ATPase activities isolated from duodenal mucosa and kidney cortex of male and female rats: preliminary study with crude enzyme samples

Effects of the s.c. administration of various doses of estradiol propionate (E.P.; 25-500 micrograms/kg) on the activities of carbonic anhydrase (CA), Mg(2+)-dependent ATPase and Mg(2+)-dependent, HCO3(-)-stimulated ATPase (Mg(2+)-HCO3(-)-ATPase) in rat duodenal mucosa and kidney cortex, and on body weight, organ weight and serum concentrations of testosterone and estradiol-17 beta, were examined in adult male, female, testectomized and ovariectomized rats. In normal male rats, activities of cytosol CA and brush border Mg(2+)-HCO3(-)-ATPase in the kidney were increased in a dose-dependent manner and reached 1.6- and 2-fold of controls, respectively, after consecutive administration (daily for 7 days) of 500 micrograms E.P. with no changes in either enzyme activities in duodenal mucosa. The positive correlations (P less than 0.01) were observed by linear regression analysis between serum concentration of estradiol-17 beta and kidney cytosol CA or kidney brush border Mg(2+)-HCO3(-)-ATPase activities. In normal female rats, activities of cytosol CA and brush border Mg(2+)-HCO3(-)-ATPase in the duodenal mucosa, and brush border Mg(2+)-HCO3(-)-ATPase activity in the kidney were increased by E.P. administration (100 and 500 micrograms/kg, daily for 7 days), however, kidney cytosol CA activity did not change by any dosage. Behavior of a part of both enzymes to E.P. in testectomized rats was altered almost in the same way to that observed in normal female rats and vice versa in ovariectomized rats. Body weight was decreased, in general, by consecutive administration of E.P. in a dose-dependent manner, and kidney weight was increased by E.P. in both male and female rats.

Evaluation of carbonic anhydrase isozymes in disorders involving osteopetrosis and/or renal tubular acidosis

Carbonic anhydrase II (CA II) deficiency in man is an autosomal recessive disorder manifest by osteopetrosis, renal tubular acidosis, and cerebral calcification. Other features include growth failure and mental retardation. Complications of the osteopetrosis include frequent bone fractures, cranial nerve compression symptoms, and dental malocclusion. The anemia and leukopenia seen in the recessive, lethal infantile form of osteopetrosis are not seen in CA II deficient patients. The renal tubular acidosis usually includes both proximal and distal components. Symptoms of metabolic acidosis respond to therapy, but no specific treatment is available for the osteopetrosis or cerebral calcification. We review here the role of carbonic anhydrases in bone resorption and renal acidification, and discuss clinical features and laboratory findings which distinguish CA II deficiency from other disorders producing osteopetrosis, renal tubular acidosis, or brain calcification. Methods to evaluate patients with pure proximal renal tubular acidosis for deficiency of CA IV are also discussed.

A novel autoantibody reactive with carbonic anhydrase in sera from patients with systemic lupus erythematosus and Sjögren's syndrome

Carbonic anhydrase (CA) is an extremely basic zinc metalloenzyme with a wide phyletic distribution, and the enzyme is important for the regulation of acid-base status. A novel autoantibody reactive with carbonic anhydrase was demonstrated. Several different classes of CA are known in mammals. Using the immuno blotting method and and immun-dot analysis, we found this autoantibody to be reactive with CA in the sera from patients with Sjögren's syndrome (20.8%), including a patient with Sjögren's syndrome and renal tubular acidosis, and in patients with systemic lupus erythematosus (31.6%). The autoantibody varied in the extent of its cross-reactivity among human CA I (or B), human CA II (or C), bovine CA I, bovine CA II, rabbit CA, and dog CA. The titers continued to float and tended to parallel disease activity. Positive reactivity of autoantibody was observed on eccrine sweat glands and the distal tubules of the kidney by the indirect immunofluorescent method.

Localization of carbonic anhydrase IV in a specific capillary bed of the human eye

Carbonic anhydrase (CA) activity plays an important role in controlling aqueous humor production in the eye and in regulating intraocular pressure. Prior studies identified the soluble isozymes CA II and CA I in the human eye and also suggested a distinct membrane-associated CA. We used an antibody to CA IV, the membrane-anchored isozyme from human lung, to study CA IV in eye tissues and to compare its distribution with that of CA II. We found intense immunostaining for CA IV associated with endothelial cells of one specific uveal capillary bed, the choriocapillaris. CA IV was not detected in endothelial cells of the contiguous capillaries of the iris or in endothelial cells of other vessels. Immunoreactivity for CA IV was also intense in epithelial and fiber cells of the lens but was not detectable in the neuroretina, the ciliary process (except for capillaries), and the cornea, all sites where immunostaining with anti-CA II antibody was intense. These studies indicate that the membrane-associated CA in human eye, which was suspected from histochemical studies, is CA IV. Defining the physiological role of this ocular isozyme remains a challenge.