Carbonic anhydrase (carbonate dehydratase) is a family of metalloenzymes (enzymes that contain one or more metal atoms as a functional component of the enzyme) that catalyze the rapid interconversion of carbon dioxide and water into carbonic acid, protons, and bicarbonate ions. This reaction occurs spontaneously in aqueous solution, but does so slowly.^[1] Carbonic anhydrase can greatly increase the rate of the reaction, with typical catalytic rates of the different forms of this enzyme ranging between 10⁴ and 10⁶ reactions per second.^[2] The active site of most carbonic anhydrases contains a zinc ion. The Enzyme Commission number (EC number) is a numerical classification scheme for enzymes, based on the chemical reactions they catalyze. ... The Enzyme Commission number (EC number) is a numerical classification scheme for enzymes, based on the chemical reactions they catalyze. ... CAS registry numbers are unique numerical identifiers for chemical compounds, polymers, biological sequences, mixtures and alloys. ... The EINECS number (for European Inventory of Existing Chemical Substances) is a registry number given to each chemical substance commercially available in the European Union between 1 January 1971 and 18 September 1981. ... It has been suggested that this article or section be merged into Catalysis. ... Carbon dioxide is a chemical compound composed of one carbon and two oxygen atoms. ... Impact of a drop of water. ... Carbonic acid (ancient name acid of air or aerial acid) has the formula H2CO3. ... In inorganic chemistry, a bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid. ... The active site of an enzyme is the binding site where catalysis occurs. ... General Name, Symbol, Number zinc, Zn, 30 Chemical series transition metals Group, Period, Block 12, 4, d Appearance bluish pale gray Atomic mass 65. ...

Structure and function of CA

Several forms of carbonic anhydrase occur in nature. In the best studied α-carbonic anhydrase form present in animals, this zinc ion is coordinated by the imidazole rings of 3 histidine residues, His94, His96 and His119. The primary function of the enzyme in animals is to interconvert carbon dioxide and bicarbonate to maintain acid-base balance in blood and other tissues and to help transport carbon dioxide out of tissues. Plants contain a different form called β-carbonic anhydrase which is an evolutionarily distinct enzyme but participates in the same reaction and also uses a zinc ion in its active site. In plants, carbonic anhydrase helps raise the concentration of CO₂ within the chloroplast to increase the carboxylation rate of the enzyme Rubisco. This is the reaction which integrates CO₂ into organic carbon sugars during photosynthesis, and can only use the CO₂ form of carbon, not carbonic acid nor bicarbonate. Divisions Green algae Chlorophyta Charophyta Land plants (embryophytes) Non-vascular plants (bryophytes) Marchantiophyta - liverworts Anthocerotophyta - hornworts Bryophyta - mosses Vascular plants (tracheophytes) †Rhyniophyta - rhyniophytes †Zosterophyllophyta - zosterophylls Lycopodiophyta - clubmosses †Trimerophytophyta - trimerophytes Pteridophyta - ferns and horsetails Seed plants (spermatophytes) †Pteridospermatophyta - seed ferns Pinophyta - conifers Cycadophyta - cycads Ginkgophyta - ginkgo Gnetophyta - gnetae Magnoliophyta - flowering plants... Chloroplasts are organelles found in plant cells and eukaryotic algae that conduct photosynthesis. ... Ribulose-1,5-bisphosphate carboxylase/oxygenase, most commonly known by the shorter name RuBisCO, is an enzyme (EC 4. ... The leaf is the primary site of photosynthesis in plants. ...

In 2000, a cadmium containing carbonic anhydrase was found to be expressed in marine diatoms during zinc limitation. In the open ocean, zinc is often in such low concentrations that it can limit the growth of phytoplankton like diatoms, thus a carbonic anhydrase using a different metal ion would be beneficial in these environments. Before this discovery, cadmium has generally been thought of as a very toxic heavy metal without biological function. As of 2005, this peculiar carbonic anhydrase form hosts the only known beneficial cadmium-dependent biological reaction. Diatoms (Greek: (dia) = through + (temnein) = to cut, i. ... Diagrams of some typical phytoplankton Phytoplankton are the autotrophic component of the plankton that drift in the water column. ... General Name, Symbol, Number cadmium, Cd, 48 Chemical series transition metals Group, Period, Block 12, 5, d Appearance silvery gray metallic Atomic mass 112. ... A heavy metal is any of a number of higher atomic weight elements, which has the properties of a metallic substance at room temperature. ...

Reactions catalyzed by carbonic anhydrase:

(in tissues - high CO₂ concentration)

(in lungs and nephrons of the kidney - low CO₂ concentration, in plant cells)

The reaction rate of carbonic anhydrase is the fastest of all enzymes, and its rate is typically limited by the diffusion rate of its substrates. Biological tissue is a collection of interconnected cells that perform a similar function within an organism. ... Respiratory system The lungs flank the heart and great vessels in the chest cavity. ... Nephron of the kidney A nephron is the basic structural and functional unit of the kidney. ... It has been suggested that Renal anomalies and Renal plasma threshold be merged into this article or section. ... A rate is a special kind of ratio, of two measurements with different units. ... This article or section does not cite its references or sources. ... In biochemistry, a substrate is a molecule upon which an enzyme acts. ...

Mechanism

Close-up rendering of active site of human carbonic anhydrase II, showing three histidine residues (in pink) and a hydroxide group (red and white) coordinating the zinc ion (purple). From PDB 1CA2.

A zinc prosthetic group in the enzyme is coordinated in three positions by histidine side chains. The fourth coordination position is occupied by water. This causes polarisation of the hydrogen-oxygen bond, making the oxygen slightly more negative, thereby weakening it. Image File history File links Download high-resolution version (1100x1044, 427 KB) Other versions Image:Carbonic anhydrase 1CA2. ... Image File history File links Download high-resolution version (1100x1044, 427 KB) Other versions Image:Carbonic anhydrase 1CA2. ... Histidine is one of the 20 most common natural amino acids present in proteins. ... Hydroxide is a polyatomic ion consisting of oxygen and hydrogen: OH− It has a charge of −1. ... General Name, Symbol, Number zinc, Zn, 30 Chemical series transition metals Group, Period, Block 12, 4, d Appearance bluish pale gray Atomic mass 65. ... The Protein Data Bank (PDB) is a repository for 3-D structural data of proteins and nucleic acids. ... General Name, Symbol, Number zinc, Zn, 30 Chemical series transition metals Group, Period, Block 12, 4, d Appearance bluish pale gray Atomic mass 65. ... A prosthetic group is a nonprotein (non-amino acid) component of a conjugated protein. ... Histidine is one of the 20 most common natural amino acids present in proteins. ... The term Side chain can have different meanings depending on the context: In chemistry and biochemistry a side chain is a part of a molecule attached to a core structure. ...

A fourth histidine is placed close to the substrate of water and accepts a proton, in an example of general acid-general base catalysis. This leaves a hydroxide attached to the zinc. // Properties [1][2] In physics, the proton (Greek proton = first) is a subatomic particle with an electric charge of one positive fundamental unit (1. ... Hydroxide is a polyatomic ion consisting of oxygen and hydrogen: OH− It has a charge of −1. ...

The active site also contains specificity pocket for carbon dioxide, bringing it close to the hydroxide group. This allows the electron rich hydroxide to attack the carbon dioxide, forming bicarbonate.

CA families

Ribbon diagram of human carbonic anhydrase II. Active site zinc ion visible at center. From PDB 1CA2.

There are at least five distinct CA families (α, β, γ, δ and ε). These families have no significant amino acid sequence similarity and in most cases are thought to be an example of convergent evolution. Image File history File links Download high-resolution version (1101x1084, 367 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Carbonic anhydrase User:Fvasconcellos/Gallery ... Image File history File links Download high-resolution version (1101x1084, 367 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Carbonic anhydrase User:Fvasconcellos/Gallery ... The active site of an enzyme is the binding site where catalysis occurs. ... General Name, Symbol, Number zinc, Zn, 30 Chemical series transition metals Group, Period, Block 12, 4, d Appearance bluish pale gray Atomic mass 65. ... The Protein Data Bank (PDB) is a repository for 3-D structural data of proteins and nucleic acids. ... Peptide sequence or amino acid sequence is the order in which amino acid residues, connected by peptide bonds, lie in the chain. ... In evolutionary biology, convergent evolution is the process whereby organisms not closely related, independently evolve similar traits as a result of having to adapt to similar environments or ecological niches. ...

α-CA

The CA enzymes found in mammals are divided into four broad subgroups: Subclasses Allotheria* Order Multituberculata (extinct) Order Volaticotheria (extinct) Order Palaeoryctoides (extinct) Order Triconodonta (extinct) Prototheria Order Monotremata Theria Infraclass Marsupialia Infraclass Eutheria The mammals are the class of vertebrate animals characterized by the production of milk in females for the nourishment of young, from mammary glands present on most species...

• the cytosolic CAs (CA-I, CA-II, CA-III, CA-VII and CA XIII)
• mitochondrial CAs (CA-VA and CA-VB)
• secreted CAs (CA-VI)
• membrane-associated CAs (CA-IV, CA-IX, CA-XII, CA-XIV and CA-XV)

The cytosol (cf. ... Electron micrograph of a mitochondrion showing its mitochondrial matrix and membranes In cell biology, a mitochondrion (plural mitochondria) (from Greek μιτος or mitos, thread + κουδριον or khondrion, granule) is a membrane-enclosed organelle, found in most eukaryotic cells. ...

β-CA

Most prokaryotic and plant chloroplast CAs belong to the beta family. Two signature patterns for this family have been identified: Prokaryotes (pro-KAR-ee-oht) (from Old Greek pro- before + karyon nut or kernel, referring to the cell nucleus, + suffix -otos, pl. ... Chloroplasts are organelles found in plant cells and eukaryotic algae that conduct photosynthesis. ... In genetics, a sequence motif is a nucleotide or amino-acid sequence pattern that is widespread and has, or is conjectured to have, a biological significance. ...

• C-[SA]-D-S-R-[LIVM]-x-[AP]
• [EQ]-[YF]-A-[LIVM]-x(2)-[LIVM]-x(4)-[LIVMF](3)-x-G-H-x(2)-C-G

γ-CA

The gamma class of CAs come from methane-producing bacteria that grow in hot springs. Methanogens are Archaea that produce methane as a metabolic by-product. ...

δ-CA

The delta class of CAs has been described in diatoms. The distinction of this class of CA has recently^[3] come into question, however. Diatoms (Greek: (dia) = through + (temnein) = to cut, i. ...

ε-CA

The epsilon class of CAs occurs exclusively in bacteria in a few chemolithotrophs and marine cyanobacteria that contain cso-carboxysomes.^[4] Recent 3-dimensional analyses^[3] suggest that ε-CA bears some structural resemblance to β-CA, particularly near the metal ion site. Thus, the two forms may be distantly related, even though the underlying amino acid sequence has since diverged considerably. Phyla Actinobacteria Aquificae Chlamydiae Bacteroidetes/Chlorobi Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Lentisphaerae Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Verrucomicrobia Bacteria (singular: bacterium) are unicellular microorganisms. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Orders The taxonomy of the Cyanobacteria is currently under revision. ... The carboxysome is a bacterial microcompartment made up of a protein shell that sequesters enzymes involved in carbon fixation reactions. ... Peptide sequence or amino acid sequence is the order in which amino acid residues, connected by peptide bonds, lie in the chain. ...

Pharmacological agents affecting CA

See Carbonic anhydrase inhibitors

Wikipedia does not yet have an article with this exact name. ...

External link

• PDB Molecule of the Month pdb49_1

The Protein Data Bank (PDB) is a repository for 3-D structural data of proteins and nucleic acids. ...

References

1. ^ Badger MR, Price GD. 1994. The role of carbonic anhydrase in photosynthesis. Annu Rev Plant Physiol Plant Mol Biol. 45:369–392
2. ^ Lindskog S. 1997. Structure and mechanism of carbonic anhydrase. PHARMACOLOGY & THERAPEUTICS. 74:1-20
3. ^ ^{a b} Sawaya MR, Cannon GC, Heinhorst S, Tanaka S, Williams EB, Yeates TO, Kerfeld CA. 2006. The structure of beta-carbonic anhydrase from the carboxysomal shell reveals a distinct subclass with one active site for the price of two. J Biol Chem. 281(11):7546-55
4. ^ So AK, Espie GS, Williams EB, Shively JM, Heinhorst S, Cannon GC. 2004. A novel evolutionary lineage of carbonic anhydrase (epsilon class) is a component of the carboxysome shell. J Bacteriol. 186(3):623-30.