Fungal oxidases

Vauquelin (14), A. Klaproth (6), and R. Jameson (5), alkali soluble organic constituents of soil and coal are designated as humic acids/ Collectively, these substances make up an ill-defined series of dark colored, weakly acidic solids which form whenever plant components (such as lignin) are exposed to fungal oxidases, or when coal is allowed to weather or otherwise oxidize. Some evidence now exists that humic acids isolated from these varied sources do indeed contain several common peripheral structures (2, II, 16), but by any more discriminating test, the term possesses little chemical significance or fixed meaning. 

Zhou G-P, hang Y, Huang X-R et al (2008) Catalytic activities of fungal oxidases in hydrophobic ionic liquid l-butyl-3-methylimidazolium hexafluorophosphate based microe-mulsion. Colloids Surf B Biointerfaces 66 146-149... 

The pH has to be controlled - the acid which is produced has to be neutralised maintaining a pH in excess of 6.0. Below pH 3.0 the glucose oxidase is inactivated and in fungal systems low pH encourages citric add production. 

Laccase, 6,699 copper, 6,654 cytochrome oxidases concerted electron transfer, 6,683 fungal... 

Copper(II) complexes with phenoxo ligands have attracted great interest, in order to develop basic coordination chemistry for their possible use as models for tyrosinase activity (dimeric complexes) and fungal enzyme galactose oxidase (GO) (monomeric complexes). The latter enzyme catalyzes the two-electron oxidation of primary alcohols with dioxygen to yield aldehyde and... 

Table 5.2 contains data about selected copper enzymes from the references noted. It should be understood that enzymes from different sources—that is, azurin from Alcaligenes denitrificans versus Pseudomonas aeruginosa, fungal versus tree laccase, or arthropodan versus molluscan hemocyanin—will differ from each other to various degrees. Azurins have similar tertiary structures—in contrast to arthropodan and molluscan hemocyanins, whose tertiary and quaternary structures show large deviations. Most copper enzymes contain one type of copper center, but laccase, ascorbate oxidase, and ceruloplasmin contain Type I, Type II, and Type III centers. For a more complete and specific listing of copper enzyme properties, see, for instance, the review article by Solomon et al.4... 

Harris, Z.L., Davis-Kaplan, S.R., Gitlin, J.D. and Kaplan, J. (2004) A fungal multicopper oxidase restores iron homeostasis in aceruloplasminemia, Blood, 103, 4672-4673. 

The redox potential of blue copper oxidases varies from species to species. The high redox potential of around 700 mV in fungal laccase is primarily attributed to nonaxial methionine ligand, a geometry that stabilizes the reduced state. Other factors such as solvent accessibility, dipole orientation, and hydrogen bonding also play an important role. ... 

Different chemical environments surrounding the T1 copper result in different redox potentials. Fungal laccases demonstrate the highest potential, close to the equilibrium potential of oxygen reduction in their respective pH regions (see Table 1). Laccases, however, are anion sensitive, with deactivation involving dissociation of T2 copper from the active site of the enzyme. Alternative copper oxidases such as bilirubin oxidase and ceruloplasmin ° ... 

Potentials vs SHE. High-surface-area carbon supports in 02-saturated buffer. Catalyzed by bilirubin oxidase in the presence of chloride. Catalyzed by fungal laccase, chloride absent. Moderate stirring by bubbled gas. Strong stirring by rotating disk electrode at 4 krpm. 

Laccase is perhaps the metallo-enzyme most widely used for this aim. Laccases are a family of multicopper ( blue copper ) oxidases widely distributed in nature Many laccases have fungal origin, while others are produced in plants. They contain four Cu(II) ions, and catalyse the one-electron oxidation of four molecules of a reducing substrate with the concomitant four-electron reduction of oxygen to water . In view of their low redox potential, which is in the range of 0.5-0.8 V vs. NHE depending on the fungal source laccases typically oxidize phenols (phenoloxidase activity) or anilines. 

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