101
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Tong CK, Chen K, Chesler M. Kinetics of activity-evoked pH transients and extracellular pH buffering in rat hippocampal slices. J Neurophysiol 2006; 95:3686-97. [PMID: 16611838 DOI: 10.1152/jn.01312.2005] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The kinetics of activity-dependent, extracellular alkaline transients, and the buffering of extracellular pH (pH(e)), were studied in rat hippocampal slices using a fluorescein-dextran probe. Orthodromic stimuli generated alkaline transients < or = 0.05 pH units that peaked in 273 +/- 26 ms and decayed with a half-time of 508 +/- 43 ms. Inhibition of extracellular carbonic anhydrase (ECA) with benzolamide increased the rate of rise by 25%, doubled peak amplitude, and prolonged the decay three- to fourfold. The slow decay in benzolamide allowed marked temporal summation, resulting in a severalfold increase in amplitude during long stimulus trains. Addition of exogenous carbonic anhydrase reduced the rate of rise, halved the peak amplitude, but had no effect on the normalized decay. A simulation of extracellular buffering kinetics generated recoveries from a base load consistent with the observed decay of the alkaline transient in the presence of benzolamide. Under control conditions, the model approximated the observed decays with an acceleration of the CO2 hydration-dehydration reactions by a factor of 2.5. These data suggest low endogenous ECA activity, insufficient to maintain equilibrium during the alkaline transients. Disequilibrium implies a time-dependent buffering capacity, with a CO2/HCO3- contribution that is small shortly after a base load. It is suggested that within 100 ms, extracellular buffering capacity is about 1% of the value at equilibrium and is provided mainly by phosphate. Accordingly, in the time frame of synaptic transmission, small base loads would generate relatively large changes in interstitial pH.
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Affiliation(s)
- Chi-Kun Tong
- Department of Physiology and Neuroscience, New York University School of Medicine, 550 First Ave., New York, New York 10016, USA
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102
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Cooper DS, Lee HJ, Yang HS, Kippen J, Yun CC, Choi I. The electroneutral sodium/bicarbonate cotransporter containing an amino terminal 123-amino-acid cassette is expressed predominantly in the heart. J Biomed Sci 2006; 13:593-5. [PMID: 16547769 PMCID: PMC1488878 DOI: 10.1007/s11373-006-9078-6] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2005] [Accepted: 02/05/2006] [Indexed: 01/12/2023] Open
Abstract
In this study, we examined the tissue-specific expression of two electroneutral Na/HCO(3) cotransporter (NBCn1) variants that differ from each other by the presence of the N-terminal 123 amino acids (cassette II). A rat Northern blot with the probe to nucleotides encoding cassette II detected a 9 kb NBCn1 mRNA strongly in the heart and weakly in skeletal muscles, but absent from most of the tissues including kidney, brain, and pancreas. In the rat heart, PCR with primers flanking cassette II preferentially amplified a DNA fragment that lacked cassette II. However, in the human heart, PCR preferentially amplified a fragment that contained cassette II. This larger PCR product was found virtually in all regions of the human cardiovascular system with strong amplification in the apex, atrium, and atrioventricular nodes. These findings indicate that the variant containing cassette II is almost absent in tissues including brain, kidney, and pancreas, where NBCn1 has been extensively examined.
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Affiliation(s)
- Deborah S. Cooper
- Department of Physiology, Emory University School of Medicine, 615 Michael Street, Atlanta, GA 30322 USA
| | - Hye Jeong Lee
- Division of Digestive Disease, Department of Medicine, Emory University School of Medicine, Atlanta, GA 30322 USA
| | - Han Soo Yang
- Department of Physiology, Emory University School of Medicine, 615 Michael Street, Atlanta, GA 30322 USA
| | - Joseph Kippen
- Department of Physiology, Emory University School of Medicine, 615 Michael Street, Atlanta, GA 30322 USA
| | - C. Chris Yun
- Division of Digestive Disease, Department of Medicine, Emory University School of Medicine, Atlanta, GA 30322 USA
| | - Inyeong Choi
- Department of Physiology, Emory University School of Medicine, 615 Michael Street, Atlanta, GA 30322 USA
- *To whom correspondence should be addressed. Fax: +1-404-727-2648; E-mail:
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103
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Li X, Liu Y, Alvarez BV, Casey JR, Fliegel L. A Novel Carbonic Anhydrase II Binding Site Regulates NHE1 Activity. Biochemistry 2006; 45:2414-24. [PMID: 16475831 DOI: 10.1021/bi051132d] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Carbonic anhydrase II (CAII) binds to and regulates transport by the NHE1 isoform of the mammalian Na(+)/H(+) exchanger. We localized and characterized the CAII binding region on the C-terminal tail of the Na(+)/H(+) exchanger. CAII did not bind to acidic sequences in NHE1 that were similar to the CAII binding site of bicarbonate transporters. Instead, by expressing a variety of fusion proteins of the C-terminal region of the Na(+)/H(+) exchanger, we demonstrated that CAII binds to the penultimate group of 13 amino acids of the cytoplasmic tail. Within this region, site-specific mutagenesis demonstrated that amino acids S796 and D797 form part of a novel CAII binding site. Phosphorylation of the C-terminal 26 amino acids by heart cell extracts did not alter CAII binding to this region, but phosphorylation greatly increased CAII binding to a protein containing the C-terminal 182 amino acids of NHE1. This suggested that an upstream region of the cytoplasmic tail acts as an inhibitor of CAII binding to the penultimate group of 13 amino acids. The results demonstrate that a novel phosphorylation-regulated CAII binding site exists in distal amino acids of the NHE1 tail.
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Affiliation(s)
- Xiuju Li
- Department of Biochemistry, 347 Medical Science Building, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
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104
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Becker HM, Hirnet D, Fecher-Trost C, Sültemeyer D, Deitmer JW. Transport Activity of MCT1 Expressed in Xenopus Oocytes Is Increased by Interaction with Carbonic Anhydrase. J Biol Chem 2005; 280:39882-9. [PMID: 16174776 DOI: 10.1074/jbc.m503081200] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Injection of carbonic anhydrase isoform II (CA) into Xenopus frog oocytes increased the rate of H+ flux via the rat monocarboxylate transporter isoform 1 (MCT1) expressed in the oocytes. MCT1 activity was assessed by changes of intracellular H+ concentration measured by pH-selective microelectrodes during application of lactate. CA-induced augmentation of the rate of H+ flux mediated by MCT1 was not inhibited by ethoxyzolamide (10 microM) and did not depend on the presence of added CO2/HCO3- but was suppressed by injection of an antibody against CA. Deleting the C terminus of the MCT1 greatly reduced its transport rate and removed transport facilitation by CA. Injected CA accelerated the CO2/HCO3(-)-induced acidification severalfold, which was blocked by ethoxyzolamide and was independent of MCT1 expression. Mass spectrometry confirmed activity of CA as injected into the frog oocytes. With pulldown assays we demonstrated a specific binding of CA to MCT1 that was not attributed to the C terminus of MCT1. Our results suggest that CA enhances MCT1 transport activity, independent of its enzymatic reaction center, presumably by binding to MCT1.
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Affiliation(s)
- Holger M Becker
- Abteilungen, Allgemeine Zoologie, Fachbereich Biologie, Technische Universität Kaiserslautern, D-67653 Kaiserslautern, Germany
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105
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Dhawan V, Schwalb DJ, Shumway MJ, Warren MC, Wexler RS, Zemtseva IS, Zifcak BM, Janero DR. Selective nitros(yl)ation induced in vivo by a nitric oxide-donating cyclooxygenase-2 inhibitor: a NObonomic analysis. Free Radic Biol Med 2005; 39:1191-207. [PMID: 16214035 DOI: 10.1016/j.freeradbiomed.2005.06.011] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/12/2005] [Revised: 06/14/2005] [Accepted: 06/20/2005] [Indexed: 11/16/2022]
Abstract
Nitric oxide (NO) enhances anti-inflammatory drug action. Through a metabonomics approach termed "NObonomics," the effects of a prototypic NO donor (organic nitrate)-cyclooxygenase-2 inhibitor hybrid (NO-coxib), NMI-1093, on the NO metabolite status of the circulation and major organs have been profiled in vivo in the rat. An oral anti-inflammatory NMI-1093 bolus elicited acute tissue-, time-, and dose-dependent changes in oxidative and nitroso/nitrosyl NO metabolites. Gastric N-nitrosation and hepatic S-nitrosation and heme nitrosylation emerged as sensitive indices of this NO-coxib's metabolism. Acute NMI-1093-induced nitros(yl)ation correlated positively as a function of nitrate plus nitrite formation across all organs examined, suggesting a unifying in vivo mechanism consequent to NMI-1093 biotransformation that links oxidative and nitros(yl)ative routes of NO chemical biology and thereby may support downstream NO signaling. NMI-1093 depressed erythrocyte nitros(yl)ation, likely by inhibiting cellular carbonic anhydrase and shifting the intracellular balance between nitrogen oxides and carbonates. Glutathione-S-transferase or cytochrome P450 inhibitors also attenuated NMI-1093's NO metabolism in a compartment-selective fashion. Although not itself a NO donor, the des-nitro coxib analog of NMI-1093 influenced basal NO metabolite profiles, implicating a cyclooxygenase-NO synthase interaction in physiological NO regulation. By detailing the global NO metrics of a unique coxib bearing a popular NO-donor pharmacophore (i.e., a nitrate moiety) and defining some critical mechanistic determinants, this study demonstrates how NObonomics can serve as valuable tool in helping elucidate NO systems biology and the effect of NO-donor and non-NO-donating therapeutics thereon.
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Affiliation(s)
- Vijay Dhawan
- NitroMed, Inc., 125 Spring Street, Lexington, MA 02421-7801, USA
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106
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Alvarez BV, Vilas GL, Casey JR. Metabolon disruption: a mechanism that regulates bicarbonate transport. EMBO J 2005; 24:2499-511. [PMID: 15990874 PMCID: PMC1176462 DOI: 10.1038/sj.emboj.7600736] [Citation(s) in RCA: 103] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2005] [Accepted: 06/08/2005] [Indexed: 02/07/2023] Open
Abstract
Carbonic anhydrases (CA) catalyze the reversible conversion of CO2 to HCO3-. Some bicarbonate transporters bind CA, forming a complex called a transport metabolon, to maximize the coupled catalytic/transport flux. SLC26A6, a plasma membrane Cl-/HCO3- exchanger with a suggested role in pancreatic HCO3- secretion, was found to bind the cytoplasmic enzyme CAII. Mutation of the identified CAII binding (CAB) site greatly reduced SLC26A6 activity, demonstrating the importance of the interaction. Regulation of SLC26A6 bicarbonate transport by protein kinase C (PKC) was investigated. Angiotensin II (AngII), which activates PKC, decreased Cl-/HCO3- exchange in cells coexpressing SLC26A6 and AT1a-AngII receptor. Activation of PKC reduced SLC26A6/CAII association in immunoprecipitates. Similarly, PKC activation displaced CAII from the plasma membrane, as monitored by immunofluorescence. Finally, mutation of a PKC site adjacent to the SLC26A6 CAB site rendered the transporter unresponsive to PKC. PKC therefore reduces CAII/SLC26A6 interaction, reducing bicarbonate transport rate. Taken together, our data support a mechanism for acute regulation of membrane transport: metabolon disruption.
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Affiliation(s)
- Bernardo V Alvarez
- Membrane Protein Research Group, Department of Physiology, University of Alberta, Edmonton, Alberta, Canada
| | - Gonzalo L Vilas
- Department of Cell Biology, University of Alberta, Edmonton, Alberta, Canada
| | - Joseph R Casey
- Membrane Protein Research Group, Department of Physiology, University of Alberta, Edmonton, Alberta, Canada
- Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada
- Department of Physiology, University of Alberta, Edmonton, Alberta, Canada T6G 2H7. Tel.: +1 780 492 7203; Fax: +1 780 492 8915; E-mail:
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107
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Nagelhus EA, Mathiisen TM, Bateman AC, Haug FM, Ottersen OP, Grubb JH, Waheed A, Sly WS. Carbonic anhydrase XIV is enriched in specific membrane domains of retinal pigment epithelium, Muller cells, and astrocytes. Proc Natl Acad Sci U S A 2005; 102:8030-5. [PMID: 15901897 PMCID: PMC1142392 DOI: 10.1073/pnas.0503021102] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Carbonic anhydrases (CAs) are ubiquitous enzymes important to many cell types throughout the body. They help determine levels of H(+) and HCO(-)(3) and thereby regulate intracellular and extracellular pH and volume. CA XIV, an extracellular membrane-bound CA, was recently shown to be present in brain and retina. Here, we analyze the subcellular distribution of CA XIV in retina by high-resolution immunogold cytochemistry and show that the distribution in retina (on glial cells but not neurons) is different from that reported for brain (on neurons but not glia). In addition, CA XIV is strongly expressed on retinal pigment epithelium (RPE). The specific membrane domains that express CA XIV were endfoot and nonendfoot membranes on Muller cells and astrocytes and apical and basolateral membranes of RPE. Gold particle density was highest on microvilli plasma membranes of RPE, where it was twice that of glial endfoot and Muller microvilli membranes and four times that of other glial membrane domains. Neither neurons nor capillary endothelial cells showed detectable labeling for CA XIV. This enrichment of CA XIV on specific membrane domains of glial cells and RPE suggests specialization for buffering pH and volume in retinal neurons and their surrounding extracellular spaces. We suggest that CA XIV is the target of CA inhibitors that enhance subretinal fluid absorption in macular edema. In addition, CA XIV may facilitate CO(2) removal from neural retina and modulate photoreceptor function.
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Affiliation(s)
- Erlend A Nagelhus
- Nordic Centre for Water Imbalance Related Disorders and Centre for Molecular Biology and Neuroscience, Institute of Basic Medical Sciences, University of Oslo, P.O. Box 1105, Blindern, N-0317 Oslo, Norway.
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108
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Innocenti A, Antel J, Wurl M, Vullo D, Firnges MA, Scozzafava A, Supuran CT. Carbonic anhydrase inhibitors. Inhibition of isozymes I, II, IV, V and IX with complex fluorides, chlorides and cyanides. Bioorg Med Chem Lett 2005; 15:1909-13. [PMID: 15780631 DOI: 10.1016/j.bmcl.2005.01.082] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2004] [Revised: 01/27/2005] [Accepted: 01/31/2005] [Indexed: 11/23/2022]
Abstract
The inhibition of five human carbonic anhydrase (hCA, EC 4.2.1.1) isozymes, the cytosolic hCA I and II, the membrane-bound hCA IV, the mitochondrial hCA V and the tumour associated, transmembrane hCA IX, with complex anions incorporating fluoride, chloride and cyanide, as well as B(III), Si(IV), P(V), As(V), Al(III), Fe(II), Fe(III), Pd(II), Pt(II), Pt(IV), Cu(I), Ag(I), Au(I) and Nb(V) species has been investigated. Apparently, the most important factors influencing activity of these complexes are the nature of the central metal ion/element, and its charge. Geometry of these compounds appears to be less important, since both linear, tetrahedral, octahedral as well as pentagonal bipyramidal derivatives led to effective inhibitors. However, the five isozymes showed very different affinities for these anion inhibitors. The best hCA I inhibitors were cyanide, dicyanocuprate and dicyanoaurate (K(I)s in the range of 0.5-7.7 microM), whereas the least effective were fluoride and hexafluoroarsenate. The best hCA II inhibitors were cyanide, hexafluoroferrate and tetrachloroplatinate (K(I)s in the range of 0.02-0.51 mM), whereas the most ineffective ones were fluoride, hexafluoroaluminate and chloride. The best hCA IV inhibitors were dicyanocuprate (K(I) of 9.8 microM) and hexacyanoferrate(II) (K(I) of 10.0 microM), whereas the worst ones were tetrafluoroborate and hexafluoroaluminate (K(I)s in the range of 124-126 mM). The most effective hCA V inhibitors were cyanide, heptafluoroniobate and dicyanocuprate (K(I)s in the range of 0.015-0.79 mM), whereas the most ineffective ones were fluoride, chloride and tetrafluoroborate (K(I)s in the range of 143-241 mM). The best hCA IX inhibitors were on the other hand cyanide, heptafluoroniobate and dicyanoargentate (K(I)s in the range of 4 microM-0.33 mM), whereas the worst ones were hexacyanoferrate(III) and hexacyanoferrate(II).
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Affiliation(s)
- Alessio Innocenti
- Università degli Studi di Firenze, Laboratorio di Chimica Bioinorganica, Rm. 188, Via della Lastruccia 3, I-50019 Sesto Fiorentino (Firenze), Italy
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109
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Innocenti A, Vullo D, Scozzafava A, Casey JR, Supuran C. Carbonic anhydrase inhibitors. Interaction of isozymes I, II, IV, V, and IX with carboxylates. Bioorg Med Chem Lett 2005; 15:573-8. [PMID: 15664815 DOI: 10.1016/j.bmcl.2004.11.057] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2004] [Revised: 11/08/2004] [Accepted: 11/18/2004] [Indexed: 11/20/2022]
Abstract
A detailed inhibition study of five carbonic anhydrase (CA, EC 4.2.1.1) isozymes with carboxylates including aliphatic (formate, acetate), dicarboxylic (oxalate, malonate), hydroxy/keto acids (l-lactate, l-malate, pyruvate), tricarboxylic (citrate), or aromatic (benzoate, tetrafluorobenzoate) representatives, some of which are important intermediates in the Krebs cycle, is presented. The cytosolic isozyme hCA I was strongly activated by acetate, oxalate, pyruvate, l-lactate, and citrate (K(A) around 0.1 microM), whereas formate, malonate, malate, and benzoate were weaker activators (K(A) in the range 0.1-1mM). The cytosolic isozyme hCA II was weakly inhibited by all the investigated anions, with inhibition constants in the range of 0.03-24 mM. The membrane-associated isozyme hCA IV was the most sensitive to inhibition by carboxylates, showing a K(I) of 99 nM for citrate and oxalate, of 2.8 microM for malonate and of 14.5 microM for pyruvate among others. The mitochondrial isozyme hCA V was weakly inhibited by all these carboxylates (K(I)s in the range of 1.67-25.9 mM), with the best inhibitor being citrate (K(I) of 1.67 mM), whereas this is the most resistant CA isozyme to pyruvate inhibition (K(I) of 5.5mM), which may be another proof that CA V is the isozyme involved in the transfer of acetyl groups from the mitochondrion to the cytosol for the provision of substrate(s) for de novo lipogenesis. Furthermore, the relative resistance of CA V to inhibition by pyruvate may be an evolutionary adaptation of this mitochondrial isozyme to the presence of high concentrations of this anion within this organelle. The transmembrane, tumor-associated isozyme hCA IX was similar to isozyme II in its slight inhibition by all these anions (K(I) in the range of 1.12-7.42 mM), except acetate, lactate, and benzoate, which showed a K(I)>150 mM. The lactate insensitivity of CA IX also represents an interesting finding, since it is presumed that this isozyme evolved in such a way as to show a high catalytic activity in hypoxic tumors rich in lactate, and suggests a possible metabolon in which CA IX participates together with the monocarboxylate/H(+) co-transporter in dealing with the high amounts of lactate/H(+) present in tumors.
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Affiliation(s)
- Alessio Innocenti
- Università degli Studi di Firenze, Laboratorio di Chimica Bioinorganica, Rm. 188, Via della Lastruccia 3, I-50019 Sesto Fiorentino (Firenze), Italy
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110
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Innocenti A, Vullo D, Scozzafava A, Supuran CT. Carbonic anhydrase inhibitors. Inhibition of isozymes I, II, IV, V, and IX with anions isosteric and isoelectronic with sulfate, nitrate, and carbonate. Bioorg Med Chem Lett 2005; 15:567-71. [PMID: 15664814 DOI: 10.1016/j.bmcl.2004.11.056] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2004] [Revised: 11/18/2004] [Accepted: 11/18/2004] [Indexed: 11/22/2022]
Abstract
The inhibition of five human carbonic anhydrase (hCA, EC 4.2.1.1) isozymes; the cytosolic hCA I and II, the membrane-bound hCA IV, the mitochondrial hCA V, and the tumor-associated, transmembrane hCA IX, with anions isosteric and isoelectronic with sulfate, nitrate, and carbonate; such as chlorate, perchlorate, bromate, iodate, periodate, silicate, bismuthate, vanadate, molybdate, and wolframate is reported. Apparently, the geometry of the inhibitor (tetrahedral or trigonal) does not influence its binding to the Zn(II) ion of the enzyme active site, but the nature of the central element is the most important factor influencing potency. Isozymes hCA I and II are best inhibited by chlorate, perchlorate, and silicate, together with the anions structurally related to sulfate, sulfamate, and sulfamidate, but sulfate itself is a weak inhibitor (inhibition constant of 74 mM against hCA I and 183 mM against hCA II). Molybdate is a very weak hCA I inhibitor (K(I) of 914 mM) but it interacts with hCA II (K(I) of 27.5mM). Isozyme IV is well inhibited by sulfate (K(I) of 9 mM), sulfamate, and sulfamidate (in the low micromolar range), but not by perchlorate (K(I) of 767 mM). The mitochondrial isozyme V has the lowest affinity for sulfate (K(I) of 680 mM) and carbonate (K(I) of 95 mM) among all the investigated isozymes, suggesting on one hand its possible participation in metabolon(s) with sulfate anion exchanger(s), and on the other hand an evolutionary adaptation to working at higher pH values (around 8.5 in mitochondria) where rather high amounts of carbonate in equilibrium with bicarbonate may be present. Metasilicate, isosteric to carbonate, is also about a 10 times weaker inhibitor of this isozyme as compared to other CAs investigated here (K(I) of 28.2 mM). Surprisingly, the tumor-associated isozyme IX is resistant to sulfate inhibition (K(I) of 154 mM) but has affinity in the low micromolar range for carbonate, sulfamate, and sulfamidate (K(I) in the range of 8.6-9.6 microM). This constitutes another proof that this isozyme best works at acidic pH values present in tumors, being inhibited substantially at higher pH values when more carbonate may be present. Bromate and chlorate are quite weak CA IX inhibitors (K(I) s of 147-274 mM).
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Affiliation(s)
- Alessio Innocenti
- Università degli Studi di Firenze, Laboratorio di Chimica Bioinorganica, Rm. 188, Via della Lastruccia 3, I-50019 Sesto Fiorentino (Firenze), Italy
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111
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Rusconi S, Innocenti A, Vullo D, Mastrolorenzo A, Scozzafava A, Supuran CT. Carbonic anhydrase inhibitors. Interaction of isozymes I, II, IV, V, and IX with phosphates, carbamoyl phosphate, and the phosphonate antiviral drug foscarnet. Bioorg Med Chem Lett 2004; 14:5763-7. [PMID: 15501037 DOI: 10.1016/j.bmcl.2004.09.064] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2004] [Revised: 09/03/2004] [Accepted: 09/17/2004] [Indexed: 12/24/2022]
Abstract
A detailed inhibition study of five carbonic anhydrase (CA, EC 4.2.1.1) isozymes with inorganic phosphates, carbamoyl phosphate, the antiviral phosphonate foscarnet as well as formate is reported. The cytosolic isozyme hCA I was weakly inhibited by neutral phosphate, strongly inhibited by carbamoyl phosphate (K(I) of 9.4 microM), and activated by hydrogen- and dihydrogenphosphate, foscarnet and formate (best activator foscarnet, K(A)=12 microM). The cytosolic isozyme hCA II was weakly inhibited by all the investigated anions, with carbamoyl phosphate showing a K(I) of 0.31 mM. The membrane-associated isozyme hCA IV was the most sensitive to inhibition by phosphates/phosphonates, showing a K(I) of 84 nM for PO(4)(3-), of 9.8 microM for HPO(4)(2-), and of 9.9 microM for carbamoyl phosphate. Foscarnet was the best inhibitor of this isozyme (K(I) of 0.82 mM) highly abundant in the kidneys, which may explain some of the renal side effects of the drug. The mitochondrial isozyme hCA V was weakly inhibited by all phosphates/phosphonates, except carbamoyl phosphate, which showed a K(I) of 8.5 microM. Thus, CA V cannot be the isozyme involved in the carbamoyl phosphate synthetase I biosynthetic reaction, as hypothesized earlier. Furthermore, the relative resistance of CA V to inhibition by inorganic phosphates suggests an evolutionary adaptation of this mitochondrial isozyme to the presence of high concentrations of such anions in these energy-converting organelles, where high amounts of ATP are produced by ATP synthetase, from ADP and inorganic phosphates. The transmembrane, tumor-associated isozyme hCA IX was on the other hand slightly inhibited by all these anions.
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Affiliation(s)
- Stefano Rusconi
- Istituto di Malattie Infettive e Tropicali, Università degli Studi di Milano, Ospedale Luigi Sacco, via G.B. Grassi 74, 20157 Milano, Italy
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112
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Innocenti A, Lehtonen JM, Parkkila S, Scozzafava A, Supuran CT. Carbonic anhydrase inhibitors. Inhibition of the newly isolated murine isozyme XIII with anions. Bioorg Med Chem Lett 2004; 14:5435-9. [PMID: 15454240 DOI: 10.1016/j.bmcl.2004.07.086] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2004] [Revised: 07/07/2004] [Accepted: 07/28/2004] [Indexed: 11/23/2022]
Abstract
The inhibition of the newly discovered cytosolic carbonic anhydrase (CA, EC 4.2.1.1) isozyme XIII of murine origin (mCA XIII) has been investigated with a series of anions, such as the physiological ones (bicarbonate, chloride), or the metal complexing anions (cyanate, cyanide, azide, hydrogen sulfide, etc), nitrate, nitrite, sulfate, sulfamate, sulfamide as well as with phenylboronic and phenylarsonic acids. The best mCA XIII inhibitors were cyanate, thiocyanate, cyanide and sulfamide, with K(I)-s in the range of 0.25microM-0.74 mM, whereas fluoride, iodide, azide, carbonate and hydrogen sulfide were less effective (K(I)-s in the range of 3.0-5.5mM). The least effective inhibitors were sulfate, chloride and bicarbonate (K(I)-s in the range of 138-267 mM). The affinity of mCA XIII for anions is very different from that of the other cytosolic isozymes (hCA I and II) or the mitochondrial isozyme hCA V. This resistance to inhibition by the physiological anions bicarbonate and chloride suggests an evolutionary adaptation of CA XIII to the presence of high concentrations of such anions (e.g., in the reproductive tract of both female and male), and the possible participation of this isozyme (similarly to CA II, CA IV and CA V) in metabolons with proteins involved in the anion exchange and transport, such as the anion exchangers (AE1-3) or the sodium bicarbonate co-transporter (NBC1 and NBC3) proteins, which remain to be identified.
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Affiliation(s)
- Alessio Innocenti
- Università degli Studi di Firenze, Laboratorio di Chimica Bioinorganica, Rm. 188, Via della Lastruccia 3, I-50019 Sesto Fiorentino (Florence), Italy
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