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Chelatase
In biochemistry, chelatases are enzymes that catalyze the insertion ("metalation") of naturally occurring tetrapyrroles. Many tetrapyrrole-based cofactors exist in nature including hemes, chlorophylls, and vitamin B12. These metallo cofactors are derived by the reaction of metal cations with tetrapyrroles, which are not ligands ''per se'', but the conjugate acids thereof. In the case of ferrochelatases, the reaction that chelatases catalyze is: :Fe2+ + H2P → FeP + 2 H+ In the above equation H2P represents a sirohydrochlorin or a porphyrin, such as protoporphyrin IX. Chelatases are required because porphyrins and related macrocyclic ligands are extremely slow to metalate, despite favorable thermodynamics. These low rates are attributed to the tight fit of the metal into the rigid 18- or 17-membered tetrapyrrole macrocycle. Several families of chelatase are known including cobalt chelatase, magnesium chelatase, and ferrochelatase. Nickel insertion into a sirohydrochlori ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ferrochelatase
Protoporphyrin ferrochelatase (EC 4.98.1.1, formerly EC 4.99.1.1, or ferrochelatase; systematic name protoheme ferro-lyase (protoporphyrin-forming)) is an enzyme encoded by the FECH gene in humans. Ferrochelatase catalyses the eighth and terminal step in the biosynthesis of heme, converting protoporphyrin IX into heme B. It catalyses the reaction: :protoheme + 2 H+ = protoporphyrin + Fe2+ Function Ferrochelatase catalyzes the insertion of ferrous iron into protoporphyrin IX in the heme biosynthesis pathway to form heme B. The enzyme is localized to the matrix-facing side of the inner mitochondrial membrane. Ferrochelatase is the best known member of a family of enzymes that add divalent metal cations to tetrapyrrole structures. For example, magnesium chelatase adds magnesium to protoporphyrin IX in the first step of bacteriochlorophyll biosynthesis. Heme B is an essential cofactor in many proteins and enzymes. In particular, heme b plays a key role as the oxygen carrie ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Magnesium Chelatase
Magnesium-chelatase is a three-component enzyme () that catalyses the insertion of Mg2+ into protoporphyrin IX. This is the first unique step in the synthesis of chlorophyll and bacteriochlorophyll. As a result, it is thought that Mg-chelatase has an important role in channeling intermediates into the (bacterio)chlorophyll branch in response to conditions suitable for photosynthetic growth: protoporphyrin IX + + ATP + \rightleftharpoons ADP + phosphate + Mg-protoporphyrin IX + 2 The four substrates of this enzyme are ATP, protoporphyrin IX, Mg2+, and H2O; its four products are ADP, phosphate, Mg-protoporphyrin IX, and H+. This enzyme belongs to the family of ligases, specifically those forming nitrogen-D-metal bonds in coordination complexes. The systematic name of this enzyme class is Mg-protoporphyrin IX magnesium-lyase. Other names in common use include protoporphyrin IX magnesium-chelatase, protoporphyrin IX Mg-chelatase, magnesium-protoporphyrin IX chelatase ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cobalt Chelatase
Cobalt chelatase () is an enzyme that catalyzes the chemical reaction :ATP + hydrogenobyrinic acid a,c-diamide + Co2+ + H2O \rightleftharpoons ADP + phosphate + cob(II)yrinic acid a,c-diamide + H+ The four substrates of this enzyme are ATP, hydrogenobyrinic acid a,c-diamide, Co2+, and H2O; its four products are ADP, phosphate, cob(II)yrinic acid a,c-diamide, and H+. The aerobic cobalt chelatase (aerobic cobalamin biosynthesis pathway) consists of three subunits, CobT, CobN () and CobS (). The macrocycle of vitamin B12 can be complexed with metal via the ATP-dependent reactions in the aerobic pathway (e.g., in ''Pseudomonas denitrificans'') or via ATP-independent reactions of sirohydrochlorin in the anaerobic pathway (e.g., in ''Salmonella typhimurium''). The corresponding cobalt chelatases are not homologous. However, aerobic cobalt chelatase subunits CobN and CobS are homologous to Mg-chelatase subunits BchH and BchI, respectively. CobT, too, has been found to be rem ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Protoporphyrin IX
Protoporphyrin IX is an organic compound, classified as a porphyrin, that plays an important role in living organisms as a precursor to other critical compounds like heme (hemoglobin) and chlorophyll. It is a deeply colored solid that is not soluble in water. The name is often abbreviated as PPIX. Protoporphyrin IX contains a porphine core, a tetrapyrrole macrocycle with a marked aromatic character. Protoporphyrin IX is essentially planar, except for the N-H bonds that are bent out of the plane of the rings, in opposite (trans) directions. Nomenclature The general term protoporphyrin refers to porphine derivatives that have the outer hydrogen atoms in the four pyrrole rings replaced by other functional groups. The prefix proto often means 'first' in science nomenclature (such as carbon protoxide), hence Hans Fischer is thought to have coined the name protoporphyrin as the first class of porphyrins. Fischer described iron-deprived heme becoming the "proto-" porphyrin, parti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Protoporphyrin IX
Protoporphyrin IX is an organic compound, classified as a porphyrin, that plays an important role in living organisms as a precursor to other critical compounds like heme (hemoglobin) and chlorophyll. It is a deeply colored solid that is not soluble in water. The name is often abbreviated as PPIX. Protoporphyrin IX contains a porphine core, a tetrapyrrole macrocycle with a marked aromatic character. Protoporphyrin IX is essentially planar, except for the N-H bonds that are bent out of the plane of the rings, in opposite (trans) directions. Nomenclature The general term protoporphyrin refers to porphine derivatives that have the outer hydrogen atoms in the four pyrrole rings replaced by other functional groups. The prefix proto often means 'first' in science nomenclature (such as carbon protoxide), hence Hans Fischer is thought to have coined the name protoporphyrin as the first class of porphyrins. Fischer described iron-deprived heme becoming the "proto-" porphyrin, parti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sirohydrochlorin
Sirohydrochlorin is a tetrapyrrole macrocyclic metabolic intermediate in the biosynthesis of sirohaem, the iron-containing prosthetic group in sulfite reductase enzymes. It is also the biosynthetic precursor to cofactor F430, an enzyme which catalyzes the release of methane in the final step of methanogenesis. Structure Sirohydrochlorin was first isolated in the early 1970s when it was shown to be the metal-free form of the prosthetic group in the ferredoxin-nitrite reductase from spinach. Its chemical identity was established by spectroscopy and by total synthesis. Biosynthesis Sirohydrochlorin is derived from a tetrapyrrolic structural framework created by the enzymes deaminase and cosynthetase which transform aminolevulinic acid via porphobilinogen and hydroxymethylbilane to uroporphyrinogen III. The latter is the first macrocyclic intermediate common to haem, chlorophyll Chlorophyll (also chlorophyl) is any of several related green pigments found in cyanobacteria and i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cofactor F430
F430 is the cofactor (sometimes called the coenzyme) of the enzyme methyl coenzyme M reductase (MCR). MCR catalyzes the reaction that releases methane in the final step of methanogenesis: : + HS–CoB → + CoB–S–S–CoM It is found only in methanogenic Archaea and anaerobic methanotrophic Archaea. It occurs in relatively high concentrations in archaea that are involved in reverse methanogenesis: these can contain up to 7% by weight of the nickel protein. Structure The trivial name cofactor F430 was assigned in 1978 based on the properties of a yellow sample extracted from '' Methanobacterium thermoautotrophicum'', which had a spectroscopic maximum at 430 nm. It was identified as the MCR cofactor in 1982 and the complete structure was deduced by X-ray crystallography and NMR spectroscopy. Coenzyme F430 features a reduced porphyrin in a macrocyclic ring system called a corphin. In addition, it possesses two additional rings in comparison to the standard tetrapyrrole ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Heme
Heme, or haem (pronounced / hi:m/ ), is a precursor to hemoglobin, which is necessary to bind oxygen in the bloodstream. Heme is biosynthesized in both the bone marrow and the liver. In biochemical terms, heme is a coordination complex "consisting of an iron ion coordinated to a porphyrin acting as a tetradentate ligand, and to one or two axial ligands." The definition is loose, and many depictions omit the axial ligands. Among the metalloporphyrins deployed by metalloproteins as prosthetic groups, heme is one of the most widely used and defines a family of proteins known as hemoproteins. Hemes are most commonly recognized as components of hemoglobin, the red pigment in blood, but are also found in a number of other biologically important hemoproteins such as myoglobin, cytochromes, catalases, heme peroxidase, and endothelial nitric oxide synthase. The word ''haem'' is derived from Greek ''haima'' meaning "blood". Function Hemoproteins have diverse biological fun ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ligases
In biochemistry, a ligase is an enzyme that can catalyze the joining ( ligation) of two large molecules by forming a new chemical bond. This is typically via hydrolysis of a small pendant chemical group on one of the larger molecules or the enzyme catalyzing the linking together of two compounds, e.g., enzymes that catalyze joining of C-O, C-S, C-N, etc. In general, a ligase catalyzes the following reaction: :Ab + C → A–C + b or sometimes :Ab + cD → A–D + b + c + d + e + f where the lowercase letters can signify the small, dependent groups. Ligase can join two complementary fragments of nucleic acid and repair single stranded breaks that arise in double stranded DNA during replication. Nomenclature The common names of ligases often include the word "ligase", such as DNA ligase, an enzyme commonly used in molecular biology laboratories to join together DNA fragments. Other common names for ligases include the word "synthetase", because they are used to synthe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Enzyme
Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. Almost all metabolic processes in the cell need enzyme catalysis in order to occur at rates fast enough to sustain life. Metabolic pathways depend upon enzymes to catalyze individual steps. The study of enzymes is called ''enzymology'' and the field of pseudoenzyme analysis recognizes that during evolution, some enzymes have lost the ability to carry out biological catalysis, which is often reflected in their amino acid sequences and unusual 'pseudocatalytic' properties. Enzymes are known to catalyze more than 5,000 biochemical reaction types. Other biocatalysts are catalytic RNA molecules, called ribozymes. Enzymes' specificity comes from their unique three-dimensional structures. Like all catalysts, enzymes increase the reac ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ligand
In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electron pairs, often through Lewis bases. The nature of metal–ligand bonding can range from covalent to ionic. Furthermore, the metal–ligand bond order can range from one to three. Ligands are viewed as Lewis bases, although rare cases are known to involve Lewis acidic "ligands". Metals and metalloids are bound to ligands in almost all circumstances, although gaseous "naked" metal ions can be generated in a high vacuum. Ligands in a complex dictate the reactivity of the central atom, including ligand substitution rates, the reactivity of the ligands themselves, and redox. Ligand selection requires critical consideration in many practical areas, including bioinorganic and medicinal chemistry, homogeneous catalysis, and environmental c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vitamin B12
Vitamin B12, also known as cobalamin, is a water-soluble vitamin involved in metabolism. It is one of eight B vitamins. It is required by animals, which use it as a cofactor in DNA synthesis, in both fatty acid and amino acid metabolism. It is important in the normal functioning of the nervous system via its role in the synthesis of myelin, and in the circulatory system in the maturation of red blood cells in the bone marrow. Plants do not need cobalamin and carry out the reactions with enzymes that are not dependent on it. Vitamin B12 is the most chemically complex of all vitamins, and for humans, the only vitamin that must be sourced from animal-derived foods or from supplements. Only some archaea and bacteria can synthesize vitamin B12. Most people in developed countries get enough B12 from the consumption of meat or foods with animal sources. Foods containing vitamin B12 include meat, clams, liver, fish, poultry, eggs, and dairy products. Many breakfast cereals a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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