Hydrogen manganese catalase

Considering all of the manganese catalases together, there have been four cluster oxidation levels that are established Mn(II,II), Mn(II,III), Mn(III,III), and Mn(III,IV). The as-isolated enzyme contains a mixture of these states. The Mn(II,II) enzyme can be prepared by the addition of hydroxylamine to the isolated enzyme. If hydrogen peroxide is added to this sample, without removing the hydroxylamine, the enzyme is converted to the Mn(III,IV) form however, if the hydroxylamine is first... 

Scheme 8. A proposed mechanism for the disproportionation of hydrogen peroxide by manganese catalase, based on the mechanism proposed by Penner-Hahn in 1992, and the T. thermophilus catalase crystal structure. [Adapted with permission from (24). Copyright 1992 WILEY-VCH Verlag.]...

Alkyl hydroperoxides, manganese, ribonucleotide reductose, hydrogen peroxide, catalase activity, tetranuclear manganese, PSII, OEC, cumene, cumene hydroperoxide, biomimetic catalysis, bioinspired catalysis, C-H activation (hydrogen activation), oxygen activation, hydroperoxide decomposition, radicals (alkyl radicals and hydroperoxy radicals) and hydrogen rebound (rebound mechanisms). 

Bacterial SODs typically contain either nonheme iron (FeSODs) or manganese (MnSODs) at their active sites, although bacterial copper/zinc and nickel SODs are also known (Imlay and Imlay 1996 Chung et al. 1999). Catalases are usually heme-containing enzymes that catalyze disproportionation of hydrogen peroxide to water and molecular oxygen (Eq. 10.2) (Zamocky and Koller 1999 Loewen et al. 2000). 

Manganese is used by nature to catalyze a number of important biological reactions that include the dismutation of superoxide radicals, the decomposition of hydrogen peroxide, and the oxidation of water to dioxygen. The dinuclear manganese centers that occur in Lactobacillus plantar-aum catalase and Thermus thermophilus catalase have attracted considerable attention and many model compounds have now been synthesized that attempt to mimic aspects of these biological systems.The catalases have at least four accessible oxidation states (Mn Mn , Mn°Mn , Mn" Mn", and Mn Mn ) it is believed that the Mn"Mn"/Mn"Mn" redox couple is effective in catalyzing the disproportionation of water. 

In part motivated by the desire to model biological redox processes, there have been many studies in which Robson-type macrocycles (205) (R = H) have been employed to form dinuclear manganese species.For example, a novel macrocyclic heterodinuclear catalase-like model complex of type (206) has been reported. " This complex can dismute hydrogen peroxide to dioxygen in basic aqueous solution. 

Catalases catalyze the conversion of hydrogen peroxide to dioxygen and water. Two families of catalases are known, one having a heme cofactor and the second a structurally distinct family, found in thermophilic and lactic acid bacteria. The manganese enzymes contain a binuclear active site and the functional form of the enzyme cycles between the (Mn )2 and the (Mn )2 oxidation states. When isolated, the enzyme is in a mixture of oxidation states including the Mn /Mn superoxidized state and this form of the enzyme has been extensively studied using XAS, UV-visible, EPR, and ESEEM spectroscopies. Multifrequency EPR and microwave polarization studies of the (Mn )2 catalytically active enzyme from L. plantarum have also been reported. ... 

Research conducted at Washington State University, as well as in situ applications by commercial entities, has indicated that stabilization of hydrogen peroxide is necessary for effective subsurface injection [39]. Without stabilization, added peroxide decomposes rapidly through interaction with iron oxyhydroxides, manganese oxyhydroxides, dissolved metals, and enzymes (e.g., peroxidase and catalase). Some of these peroxide decay pathways involve nonhydroxyl radical-forming mechanisms, and therefore are especially detrimental to Fenton oxidation systems. 

There are a number of enzymes that catalyse the dismutation of superoxide in vivo, viz. the superoxide dismutases [50,51], They are metalloproteins which contain copper, zinc, manganese or iron as the prosthetic group. The enzyme catalase exists in vivo to degrade hydrogen peroxide within cells to form water and oxygen [43]. As stated earlier, there are barely detectable amounts of these two enzymes in the synovial fluid of arthritic patients and hence both superoxide radicals and hydrogen peroxide are potential mediators of damage to the biomolecules of the synovial fluid. 

Manganese is required by mitochondrial superoxide dismutase. This enzyme catalyzes the same reaction catalyzed by the cytosolic form of the enzyme, namely the conversion of superoxide to hydrogen peroxide. Superoxide is a molecule of oxygen containing one additional electron. It is produced as a byproduct of various reactions in which molecular oxygen (O ) is involved. These reactions may include those of cytochrome c oxidase and various flavoproteins- The HOOH formed by superoxide is decomposed by catalase ... 

Catalase is a more effective catalyst on this reaction than manganese(I V) oxide. This can be shown by adding a piece of liver or liquidised celery (which both contain catalase) to a solution of hydrogen peroxide and observing that oxygen gas is evolved instantly and dramatically. 

Enzymes are long-chain proteins that have a complicated structure and normally have only one particular site at which a reaction can take place. X-Ray diffraction results have shown that this region, called the active site, has a definite shape for each enzyme, and therefore only molecules with a similar complementary shape will fit into it - rather like keys in a lock. For example, only hydrogen peroxide molecules will fit the active site of catalase. Those molecules that do fit the active site are called substrate molecules. Thus, enzymes are much more specific catalysts than inorganic substances such as manganese(IV) oxide. 

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