carbon-monoxide dehydrogenase (acceptor) | |||||||||
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Identifiers | |||||||||
EC no. | 1.2.7.4 | ||||||||
CAS no. | 64972-88-9 | ||||||||
Databases | |||||||||
IntEnz | IntEnz view | ||||||||
BRENDA | BRENDA entry | ||||||||
ExPASy | NiceZyme view | ||||||||
KEGG | KEGG entry | ||||||||
MetaCyc | metabolic pathway | ||||||||
PRIAM | profile | ||||||||
PDB structures | RCSB PDB PDBe PDBsum | ||||||||
Gene Ontology | AmiGO / QuickGO | ||||||||
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In enzymology, carbon monoxide dehydrogenase (CODH) (EC 1.2.7.4) is an enzyme that catalyzes the chemical reaction
The chemical process catalyzed by carbon monoxide dehydrogenase is similar to the water-gas shift reaction.
The 3 substrates of this enzyme are CO, H2O, and A, whereas its two products are CO2 and AH2.
A variety of electron donors/receivers (Shown as "A" and "AH2" in the reaction equation above) are observed in micro-organisms which utilize CODH. Several examples of electron transfer cofactors have been proposed, including Ferredoxin, NADP+/NADPH and flavoprotein complexes like flavin adenine dinucleotide (FAD) as well as hydrogenases. [1] [2] [3] [4] CODHs support the metabolisms of diverse prokaryotes, including methanogens, aerobic carboxidotrophs, acetogens, sulfate-reducers, and hydrogenogenic bacteria. The bidirectional reaction catalyzed by CODH plays a role in the carbon cycle allowing organisms to both make use of CO as a source of energy and utilize CO2 as a source of carbon. CODH can form a monofunctional enzyme, as is the case in Rhodospirillum rubrum, or can form a cluster with acetyl-CoA synthase as has been shown in M. thermoacetica. When acting in concert, either as structurally independent enzymes or in a bifunctional CODH/ACS unit, the two catalytic sites are key to carbon fixation in the reductive acetyl-CoA pathway. Microbial organisms (Both aerobic and anaerobic) encode and synthesize CODH for the purpose of carbon fixation (CO oxidation and CO2 reduction). Depending on attached accessory proteins (A,B,C,D-Clusters), serve a variety of catalytic functions, including reduction of [4Fe-4S] clusters and insertion of nickel. [5]
This enzyme belongs to the family of oxidoreductases, specifically those acting on the aldehyde or oxo group of donor with other acceptors. The systematic name of this enzyme class is carbon-monoxide:acceptor oxidoreductase. Other names in common use include anaerobic carbon monoxide dehydrogenase, carbon monoxide oxygenase, carbon-monoxide dehydrogenase, and carbon-monoxide:(acceptor) oxidoreductase.
CODH are a rather diverse group of enzymes, containing two unrelated types of CODH. A copper-molybdenum flavoenzymes is found in some aerobic carboxydotrophic bacteria. Anaerobic bacteria utilize nickel-iron based CODHs. [6] [7] [8] Both classes of CODH catalyze the conversion of carbon monoxide (CO) to carbon dioxide (CO2). Only the Ni containing CODH is able to also catalyze the back reaction. CODHs exist in both monofunctional and bifunctional forms. An example for the latter case, Ni,Fe-CODHs form a bifunctional cluster with acetyl-CoA synthase, as has been well characterized in the anaerobic bacteria Moorella thermoacetica, [9] [10] Clostridium autoethanogenum [11] and Carboxydothermus hydrogenoformans [12] . While the ACS subunits of the complex of C. autoethanogenum show a rather extended arrangement [11] those of the M. thermoacetica and C. hydrogenoformans complex are closer to the CODH subunits forming a tight tunnel network connecting cluster C and cluster A. [13] [12]
Nickel containing CODH (Ni,Fe-CODH) can be further divided into structural clades, dependent on their phylogenetic relationship [14]
Homodimeric Ni,Fe-CODHs contain five-metal clusters. [15] They exist either in a homodimeric form (also called monofunctional) or in a bifunctional α2β2-tetrameric complex with acetyl-CoA synthase (ACS).
The best studied monofunctional CODHs are those of Desulfovibrio vulgaris, [15] Rhodospirillum rubrum [16] [17] and Carboxydothermus hydrogenoformans. [18] [19] [7] They are homodimers of around 130 kDa sharing a central [4Fe4S]-cluster at the surface of the protein - cluster D. The electrons are probably transferred to another [4Fe4S]-cluster (cluster B) located 10 A inside the protein and from there to the active site - cluster C, being an [Ni4Fe4S]-cluster. [7] [17]
The CODH/ACS complex is an α2β2 tetrameric enzyme. The structures of CODH/ACS complexes of the anaerobic bacteria Moorella thermoacetica, [9] [10] Clostridium autoethanogenum [11] and Carboxydothermus hydrogenoformans [12] have been solved. The two CODH subunits form the central core of the enzyme to which an ACS subunit is attached at each side. Each α unit contains a single metal cluster. Together, the two β units contains five clusters of three types. CODH catalytic activity occurs at the Ni-[3Fe-4S] C-clusters while the interior [4Fe-4S] B and D clusters transfer electrons away from the C-cluster to external electron carriers such as ferredoxin. The ACS activity occurs in A-cluster located in the outer two α units. [7] [8]
All CODH/ACS complexes have a gas tunnel connecting the multiple active sites, while the tunnel system in the C. autoethanogenum enzyme is comparatively open and those of M. thermoacetica and C. hydrogenoformans rather tight. [9] [11] [12] For the Moorella enzyme the rate of acetyl-CoA synthase activity from CO2 is not affected by the addition of hemoglobin, which would compete for CO in bulk solution, [13] and isotopic labeling studies show that carbon monoxide derived from the C-cluster is preferentially used at the A-cluster over unlabeled CO in solution. [20] Protein engineering of the CODH/ACS in M.thermoacetica revealed that mutating residues, so as to functionally block the tunnel, stopped acetyl-CoA synthesis when only CO2 was present. [21] The discovery of a functional CO tunnel places CODH on a growing list of enzymes that independently evolved this strategy to transfer reactive intermediates from one active site to another. [22]
The CODH catalytic site, referred to as the C-cluster, is a [3Fe-4S] cluster bonded to a Ni-Fe moiety. Two basic amino acids (Lys587 and His 113 in M.thermoacetica) reside in proximity to the C-cluster and facilitate acid-base chemistry required for enzyme activity. [23] Furthermore, other residues (i.e. an isoleucine apical to the Ni atom) fine-tune the binding and conversion of CO. [24] Based on IR spectra suggesting the presence of an Ni-CO complex, the proposed first step in the oxidative catalysis of CO to CO2 involves the binding of CO to Ni2+ and corresponding complexing of Fe2+ to a water molecule. [25]
It has been proposed that CO binds to square-planar nickel where it converts to a carboxy bridge between the Ni and Fe atom. [7] [26] A decarboxylation leads to the release of CO2 and the reduction of the cluster.
The electrons in the reduced C-cluster are transferred to nearby B and D [4Fe-4S] clusters, returning the Ni-[3Fe-4S] C-cluster to an oxidized state and reducing the single electron carrier ferredoxin. [27] [28]
Given CODH's role in CO2 fixation, the reductive mechanism is sometimes inferred as the “direct reverse” of the oxidative mechanism by the ”principle of microreversibility.” [29]
Carbon monoxide dehydrogenase regulates atmospheric CO and CO2 levels. Anaerobic micro-organisms like Acetogens undergo the Wood-Ljungdahl Pathway, relying on CODH to produce CO by reduction of CO2 needed for the synthesis of Acetyl-CoA from a methyl, coenzyme a (CoA) and corrinoid iron-sulfur protein. [29] Other types show CODH being utilized to generate a proton motive force for the purposes of energy generation. CODH is used for the CO oxidation, producing two protons which are subsequently reduced to form dihydrogen (H2. [30]
The citric acid cycle—also known as the Krebs cycle, Szent–Györgyi–Krebs cycle or the TCA cycle (tricarboxylic acid cycle)—is a series of biochemical reactions to release the energy stored in nutrients through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins. The chemical energy released is available under the form of ATP. The Krebs cycle is used by organisms that respire (as opposed to organisms that ferment) to generate energy, either by anaerobic respiration or aerobic respiration. In addition, the cycle provides precursors of certain amino acids, as well as the reducing agent NADH, that are used in numerous other reactions. Its central importance to many biochemical pathways suggests that it was one of the earliest components of metabolism. Even though it is branded as a "cycle", it is not necessary for metabolites to follow only one specific route; at least three alternative segments of the citric acid cycle have been recognized.
Cytochromes P450 are a superfamily of enzymes containing heme as a cofactor that mostly, but not exclusively, function as monooxygenases. However, they are not omnipresent; for example, they have not been found in Escherichia coli. In mammals, these enzymes oxidize steroids, fatty acids, xenobiotics, and participate in many biosyntheses. By hydroxylation, CYP450 enzymes convert xenobiotics into hydrophilic derivatives, which are more readily excreted.
Biological carbon fixation, or сarbon assimilation, is the process by which living organisms convert inorganic carbon to organic compounds. These organic compounds are then used to store energy and as structures for other biomolecules. Carbon is primarily fixed through photosynthesis, but some organisms use chemosynthesis in the absence of sunlight. Chemosynthesis is carbon fixation driven by chemical energy rather than from sunlight.
Ferredoxins are iron–sulfur proteins that mediate electron transfer in a range of metabolic reactions. The term "ferredoxin" was coined by D.C. Wharton of the DuPont Co. and applied to the "iron protein" first purified in 1962 by Mortenson, Valentine, and Carnahan from the anaerobic bacterium Clostridium pasteurianum.
Iron–sulfur proteins are proteins characterized by the presence of iron–sulfur clusters containing sulfide-linked di-, tri-, and tetrairon centers in variable oxidation states. Iron–sulfur clusters are found in a variety of metalloproteins, such as the ferredoxins, as well as NADH dehydrogenase, hydrogenases, coenzyme Q – cytochrome c reductase, succinate – coenzyme Q reductase and nitrogenase. Iron–sulfur clusters are best known for their role in the oxidation-reduction reactions of electron transport in mitochondria and chloroplasts. Both Complex I and Complex II of oxidative phosphorylation have multiple Fe–S clusters. They have many other functions including catalysis as illustrated by aconitase, generation of radicals as illustrated by SAM-dependent enzymes, and as sulfur donors in the biosynthesis of lipoic acid and biotin. Additionally, some Fe–S proteins regulate gene expression. Fe–S proteins are vulnerable to attack by biogenic nitric oxide, forming dinitrosyl iron complexes. In most Fe–S proteins, the terminal ligands on Fe are thiolate, but exceptions exist.
A hydrogenase is an enzyme that catalyses the reversible oxidation of molecular hydrogen (H2), as shown below:
Acetogenesis is a process through which acetate is produced by prokaryote microorganisms either by the reduction of CO2 or by the reduction of organic acids, rather than by the oxidative breakdown of carbohydrates or ethanol, as with acetic acid bacteria.
Citrate synthase is an enzyme that exists in nearly all living cells. It functions as a pace-making enzyme in the first step of the citric acid cycle. Citrate synthase is located within eukaryotic cells in the mitochondrial matrix, but is encoded by nuclear DNA rather than mitochondrial. It is synthesized using cytoplasmic ribosomes, then transported into the mitochondrial matrix.
Bioorganometallic chemistry is the study of biologically active molecules that contain carbon directly bonded to metals or metalloids. The importance of main-group and transition-metal centers has long been recognized as important to the function of enzymes and other biomolecules. However, only a small subset of naturally-occurring metal complexes and synthetically prepared pharmaceuticals are organometallic; that is, they feature a direct covalent bond between the metal(loid) and a carbon atom. The first, and for a long time, the only examples of naturally occurring bioorganometallic compounds were the cobalamin cofactors (vitamin B12) in its various forms. In the 21st century, as a result of the discovery of new systems containing carbon–metal bonds in biology, bioorganometallic chemistry is rapidly emerging as a distinct subdiscipline of bioinorganic chemistry that straddles organometallic chemistry and biochemistry. Naturally occurring bioorganometallics include enzymes and sensor proteins. Also within this realm are synthetically prepared organometallic compounds that serve as new drugs and imaging agents (technetium-99m sestamibi) as well as the principles relevant to the toxicology of organometallic compounds (e.g., methylmercury). Consequently, bioorganometallic chemistry is increasingly relevant to medicine and pharmacology.
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The Wood–Ljungdahl pathway is a set of biochemical reactions used by some bacteria. It is also known as the reductive acetyl-coenzyme A (acetyl-CoA) pathway. This pathway enables these organisms to use hydrogen as an electron donor, and carbon dioxide as an electron acceptor and as a building block for biosynthesis.
Formate dehydrogenases are a set of enzymes that catalyse the oxidation of formate to carbon dioxide, donating the electrons to a second substrate, such as NAD+ in formate:NAD+ oxidoreductase (EC 1.17.1.9) or to a cytochrome in formate:ferricytochrome-b1 oxidoreductase (EC 1.2.2.1). This family of enzymes has attracted attention as inspiration or guidance on methods for the carbon dioxide fixation, relevant to global warming.
In enzymology, a carbon-monoxide dehydrogenase (ferredoxin) (EC 1.2.7.4) is an enzyme that catalyzes the chemical reaction
In enzymology, a pyruvate synthase is an enzyme that catalyzes the interconversion of pyruvate and acetyl-CoA. It is also called pyruvate:ferredoxin oxidoreductase (PFOR).
Biotin synthase (BioB) is an enzyme that catalyzes the conversion of dethiobiotin (DTB) to biotin; this is the final step in the biotin biosynthetic pathway. Biotin, also known as vitamin B7, is a cofactor used in carboxylation, decarboxylation, and transcarboxylation reactions in many organisms including humans. Biotin synthase is an S-Adenosylmethionine (SAM) dependent enzyme that employs a radical mechanism to thiolate dethiobiotin, thus converting it to biotin.
Radical SAM enzymes belong to a superfamily of enzymes that use an iron-sulfur cluster (4Fe-4S) to reductively cleave S-adenosyl-L-methionine (SAM) to generate a radical, usually a 5′-deoxyadenosyl radical (5'-dAdo), as a critical intermediate. These enzymes utilize this radical intermediate to perform diverse transformations, often to functionalize unactivated C-H bonds. Radical SAM enzymes are involved in cofactor biosynthesis, enzyme activation, peptide modification, post-transcriptional and post-translational modifications, metalloprotein cluster formation, tRNA modification, lipid metabolism, biosynthesis of antibiotics and natural products etc. The vast majority of known radical SAM enzymes belong to the radical SAM superfamily, and have a cysteine-rich motif that matches or resembles CxxxCxxC. Radical SAM enzymes comprise the largest superfamily of metal-containing enzymes.
Oxalate oxidoreductases (EC 1.2.7.10) (OOR) are a relatively recently discovered group of enzymes that break down oxalate, a problematic molecule nutritionally. The first one to have been characterized has the systematic name oxalate:ferredoxin oxidoreductase. This enzyme catalyses the following chemical reaction:
FeMoco (FeMo cofactor) is the primary cofactor of nitrogenase. Nitrogenase is the enzyme that catalyzes the conversion of atmospheric nitrogen molecules N2 into ammonia (NH3) through the process known as nitrogen fixation. Because it contains iron and molybdenum, the cofactor is called FeMoco. Its stoichiometry is Fe7MoS9C.
Acetyl-CoA synthase (ACS), not to be confused with acetyl-CoA synthetase or acetate-CoA ligase, is a nickel-containing enzyme involved in the metabolic processes of cells. Together with carbon monoxide dehydrogenase (CODH), it forms the bifunctional enzyme Acetyl-CoA Synthase/Carbon Monoxide Dehydrogenase (ACS/CODH) found in anaerobic microorganisms such as archaea and bacteria. The ACS/CODH enzyme works primarily through the Wood–Ljungdahl pathway which converts carbon dioxide to Acetyl-CoA. The recommended name for this enzyme is CO-methylating acetyl-CoA synthase.
In enzymology, a formylmethanofuran dehydrogenase (EC 1.2.99.5) is an enzyme that catalyzes the chemical reaction:
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