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Ascorbate Peroxidase
Ascorbate peroxidase (or L-ascorbate peroxidase, APX) () is an enzyme that catalyzes the chemical reaction :L-ascorbate + H2O2 \rightleftharpoons dehydroascorbate + 2 H2O It is a member of the family of heme-containing peroxidases. Heme peroxidases catalyse the H2O2-dependent oxidation of a wide range of different, usually organic, substrates in biology. This enzyme belongs to the family of oxidoreductases, specifically those acting on a peroxide as acceptor (peroxidases). The systematic name of this enzyme class is L-ascorbate:hydrogen-peroxide oxidoreductase. Other names in common use include L-ascorbic acid peroxidase, L-ascorbic acid-specific peroxidase, ascorbate peroxidase, and ascorbic acid peroxidase. This enzyme participates in ascorbate and aldarate metabolism. Overview Ascorbate-dependent peroxidase activity was first reported in 1979,, more than 150 years after the first observation of peroxidase activity in horseradish plants and almost 40 years after the disco ... [...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 reaction ra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Monodehydroascorbate Reductase (NADH)
In enzymology, a monodehydroascorbate reductase (MDAR) () is an enzyme that catalyzes the chemical reaction :NADH + H+ + 2 monodehydroascorbate \rightleftharpoons NAD+ + 2 ascorbate The 3 substrates of this enzyme are NADH, H+, and monodehydroascorbate, whereas its two products are NAD+ and ascorbate. This enzyme belongs to the family of oxidoreductases, specifically those acting on NADH or NADPH, with a quinone or similar compound as an acceptor. The systematic name of this enzyme class is NADH: monodehydroascorbate oxidoreductase. Other names in common use include NADH: semidehydroascorbic acid oxidoreductase, MDHA, semidehydroascorbate reductase, AFR, AFR-reductase, ascorbic free radical reductase, ascorbate free radical reductase, SOR, MDAsA reductase (NADPH), SDA reductase, NADH: ascorbate radical oxidoreductase, NADH-semidehydroascorbate oxidoreductase, ascorbate free-radical reductase, NADH: AFR oxidoreductase, and monodehydroascorbate reductase (NADH2). This enzyme p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Manganese Peroxidase
Manganese is a chemical element with the symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of industrial alloy uses, particularly in stainless steels. It improves strength, workability, and resistance to wear. Manganese oxide is used as an oxidising agent; as a rubber additive; and in glass making, fertilisers, and ceramics. Manganese sulfate can be used as a fungicide. Manganese is also an essential human dietary element, important in macronutrient metabolism, bone formation, and free radical defense systems. It is a critical component in dozens of proteins and enzymes. It is found mostly in the bones, but also the liver, kidneys, and brain. In the human brain, the manganese is bound to manganese metalloproteins, most notably glutamine synthetase in astrocytes. Manganese was first isolated in 1774. It is familiar in the laboratory in the form of the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cytochrome C Peroxidase
Cytochrome ''c'' peroxidase, or CCP, is a water-soluble heme-containing enzyme of the peroxidase family that takes reducing equivalents from cytochrome ''c'' and reduces hydrogen peroxide to water: :CCP + H2O2 + 2 ferrocytochrome ''c'' + 2H+ → CCP + 2H2O + 2 ferricytochrome ''c'' CCP can be derived from aerobically grown yeast strains and can be isolated in both native and recombinant forms with high yield from ''Saccharomyces cerevisiae.'' The enzyme’s primary function is to eliminate toxic radical molecules produced by the cell which are harmful to biological systems. It works to maintain low concentration levels of hydrogen peroxide, which is generated by the organism naturally through incomplete oxygen reduction. When glucose levels in fast growing yeast strains are exhausted, the cells turn to respiration which raises the concentration of mitochondrial H2O2. In addition to its peroxidase activity, it acts as a sensor and a signaling molecule to exogenous H2O2, which acti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Protein Data Bank
The Protein Data Bank (PDB) is a database for the three-dimensional structural data of large biological molecules, such as proteins and nucleic acids. The data, typically obtained by X-ray crystallography, NMR spectroscopy, or, increasingly, cryo-electron microscopy, and submitted by biologists and biochemists from around the world, are freely accessible on the Internet via the websites of its member organisations (PDBe, PDBj, RCSB, and BMRB). The PDB is overseen by an organization called the Worldwide Protein Data Bank, wwPDB. The PDB is a key in areas of structural biology, such as structural genomics. Most major scientific journals and some funding agencies now require scientists to submit their structure data to the PDB. Many other databases use protein structures deposited in the PDB. For example, SCOP and CATH classify protein structures, while PDBsum provides a graphic overview of PDB entries using information from other sources, such as Gene ontology. History Two force ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tertiary Structure
Protein tertiary structure is the three dimensional shape of a protein. The tertiary structure will have a single polypeptide chain "backbone" with one or more protein secondary structures, the protein domains. Amino acid side chains may interact and bond in a number of ways. The interactions and bonds of side chains within a particular protein determine its tertiary structure. The protein tertiary structure is defined by its atomic coordinates. These coordinates may refer either to a protein domain or to the entire tertiary structure.Branden C. and Tooze J. "Introduction to Protein Structure" Garland Publishing, New York. 1990 and 1991. A number of tertiary structures may fold into a quaternary structure.Kyte, J. "Structure in Protein Chemistry." Garland Publishing, New York. 1995. History The science of the tertiary structure of proteins has progressed from one of hypothesis to one of detailed definition. Although Emil Fischer had suggested proteins were made of polypept ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Porphyrin
Porphyrins ( ) are a group of heterocyclic macrocycle organic compounds, composed of four modified pyrrole subunits interconnected at their α carbon atoms via methine bridges (=CH−). The parent of porphyrin is porphine, a rare chemical compound of exclusively theoretical interest. Substituted porphines are called porphyrins. With a total of 26 π-electrons, of which 18 π-electrons form a planar, continuous cycle, the porphyrin ring structure is often described as aromatic. One result of the large conjugated system is that porphyrins typically absorb strongly in the visible region of the electromagnetic spectrum, i.e. they are deeply colored. The name "porphyrin" derives from the Greek word πορφύρα (''porphyra''), meaning ''purple''. Complexes of porphyrins Concomitant with the displacement of two N-''H'' protons, porphyrins bind metal ions in the N4 "pocket". The metal ion usually has a charge of 2+ or 3+. A schematic equation for these syntheses is shown: :H2porp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
High-valent Iron
High-valent iron commonly denotes compounds and intermediates in which iron is found in a formal oxidation state > 3 that show a number of bonds > 6 with a coordination number ≤ 6. The term is rather uncommon for hepta-coordinate compounds of iron. It has to be distinguished from the terms hypervalent and hypercoordinate, as high-valent iron compounds neither necessarily violate the 18-electron rule nor necessarily show coordination numbers > 6. The ferrate(VI) ion eO4sup>2− was the first structure in this class synthesized. The synthetic compounds discussed below contain highly oxidized iron in general, as the concepts are closely related. Oxoiron compounds Oxoferryl species are commonly proposed as intermediates in catalytic cycles, especially biological systems in which O2 activation is required. Diatomic oxygen has a high reduction potential (E0 = 1.23 V), but the first step required to harness this potential is a thermodynamically unfavorable one electron reduction E0 = ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Horseradish Peroxidase
The enzyme horseradish peroxidase (HRP), found in the roots of horseradish, is used extensively in biochemistry applications. It is a metalloenzyme with many isoforms, of which the most studied type is C. It catalyzes the oxidation of various organic substrates by hydrogen peroxide. Structure The structure of the enzyme was first solved by X-ray crystallography in 1997; and has since been solved several times with various substrates. It is a large alpha-helical glycoprotein which binds heme as a redox cofactor. Substrates Alone, the HRP enzyme, or conjugates thereof, is of little value; its presence must be made visible using a substrate that, when oxidized by HRP using hydrogen peroxide as the oxidizing agent, yields a characteristic color change that is detectable by spectrophotometric methods. Numerous substrates for horseradish peroxidase have been described and commercialized to exploit the desirable features of HRP. These substrates fall into several distinct cat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Glutathione-ascorbate Cycle
The ascorbate-glutathione cycle, sometimes Foyer-Halliwell- Asada pathway, is a metabolic pathway that detoxifies hydrogen peroxide (H2O2), a reactive oxygen species that is produced as a waste product in metabolism. The cycle involves the antioxidant metabolites: ascorbate, glutathione and NADPH and the enzymes linking these metabolites. In the first step of this pathway, H2O2 is reduced to water by ascorbate peroxidase (APX) using ascorbate (ASC) as the electron donor. The oxidized ascorbate (monodehydroascorbate, MDA) is regenerated by monodehydroascorbate reductase (MDAR). However, monodehydroascorbate is a radical and if not rapidly reduced it disproportionates into ascorbate and dehydroascorbate (DHA). Dehydroascorbate is reduced to ascorbate by dehydroascorbate reductase (DHAR) at the expense of GSH, yielding oxidized glutathione (GSSG). Finally GSSG is reduced by glutathione reductase (GR) using NADPH as the electron donor. Thus ascorbate and glutathione are not consume ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ascorbate
Vitamin C (also known as ascorbic acid and ascorbate) is a water-soluble vitamin found in citrus and other fruits and vegetables, also sold as a dietary supplement and as a topical 'serum' ingredient to treat melasma (dark pigment spots) and wrinkles on the face. It is used to prevent and treat scurvy. Vitamin C is an essential nutrient involved in the repair of tissue, the formation of collagen, and the enzymatic production of certain neurotransmitters. It is required for the functioning of several enzymes and is important for immune system function. It also functions as an antioxidant. Most animals are able to synthesize their own vitamin C. However, apes (including humans) and monkeys (but not all primates), most bats, some rodents, and certain other animals must acquire it from dietary sources. There is some evidence that regular use of supplements may reduce the duration of the common cold, but it does not appear to prevent infection. It is unclear whether supplementa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Catalysis
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quickly, very small amounts of catalyst often suffice; mixing, surface area, and temperature are important factors in reaction rate. Catalysts generally react with one or more reactants to form intermediates that subsequently give the final reaction product, in the process of regenerating the catalyst. Catalysis may be classified as either homogeneous, whose components are dispersed in the same phase (usually gaseous or liquid) as the reactant, or heterogeneous, whose components are not in the same phase. Enzymes and other biocatalysts are often considered as a third category. Catalysis is ubiquitous in chemical industry of all kinds. Estimates are that 90% of all commercially produced chemical products involve catalysts at some s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
