Peroxidases extracellular

Choi H.W. Kim Y.J. Lee S.C. Hong J.K. Hwang B.K. (2007) Hydrogen peroxide generation by the pepper extracellular peroxidase CaP02 activates local and systemic cell death and defense response to bacterial pathogens / / Plant Physiology. V. 145. P. 890-904. 

Figure 42-11. Model of iodide metabolism in the thyroid follicle. A follicular cell is shown facing the follicular lumen (top) and the extracellular space (at bottom). Iodide enters the thyroid primarily through a transporter (bottom left). Thyroid hormone synthesis occurs in the follicular space through a series of reactions, many of which are peroxidase-mediated. Thyroid hormones, stored in the colloid in the follicular space, are released from thyroglobulin by hydrolysis inside the thyroid cell. (Tgb, thyroglobulin MIT, monoiodotyrosine DIT, diiodotyro-sine Tj, triiodothyronine T4, tetraiodothyronine.) Asterisks indicate steps or processes that are inherited enzyme deficiencies which cause congenital goiter and often result in hypothyroidism.

Urzua U, PJ Kersten, R Vicuna (1998) Manganese peroxidase-dependent oxidation of glycolic and oxalic acids synthesized by Ceriporiopsis subvermispora produces extracellular hydrogen peroxide. Appl Environ Microbiol 64 68-73. 

The class II secreted fungal heme peroxidases include the LMPs LiP, MnP and VP [70]. All of these enzymes are extracellular and contain protoporphyrin IX (heme) as prosthetic group. They use H2O2 or organic hydroperoxides as electron accepting cosubstrates during the oxidation of diverse compounds. They are secreted as glycosilated, 35-38 kDa size proteins. 

Although the exact mechanism of degradation at metabolic level for each compound or group of compounds is not well known, the involvement of extracellular oxidative enzymes such as LAC, MnP, LiP, and versatile peroxidase (VP) (see Tables 1 and 2 of Chap. 6) and intracellular monooxygenases as cytochrome P-450 is well documented for pollutants such as hydrocarbons, dyes, and halogenated solvents [25]. To determine the actual role of the extracellular enzymes, many studies are performed in vitro experiments with purified enzymes. In the case of cytochrome P-450, usually inhibitors are used. 

Hofrichter, M., and Fritsche, W., Depolymerization of Low-Rank Coal by Extracellular Fungal Enzyme Systems. 3. In Vitro Depolymerization of Coal Humic Acids by a Crude Preparation of Manganese Peroxidase From the White-Rot Fungus Nematoloma Frowardii B19. Applied Microbiology and Biotechnology, 1997. 47(5) pp. 566-571. 

Extracellular peroxidases are produced by Streptomyces chromofuscus, with the capability to decolorize azo dyes associated to ligninolytic activity in aerobiosis. Azo dyes are converted to cationic radicals, which are subjected to nucleophilic attack by water or hydrogen peroxide molecules, producing reactive compounds that undergo redox reactions that result in a more stable intermediate [37]. 

Horseradish peroxidase (HRP) is an extracellular plant enzyme that acts in regulation of cell growth and differentiation, polymerization of cell wall components, and the oxidation of secondary metabolites essential for important pathogenic defense reactions. Because of these essential functions, and also because of its stability and ready availability, HRP has attracted considerable attention.13 It has been involved in a number of applications, such as diagnostic assays,14 biosensors,15 bioremediation,16 polymer synthesis,17 and other biotechnological processes.18 More applications in which HRP catalysis is translated into an electrochemical signal are likely to be developed in the near future. 

Figure 5.11. Reactive oxidant production by human neutrophils. In (a), neutrophils (5 x lOVml) were suspended in buffer containing 10 pM luminol in the presence and absence of a mixture of the extracellular oxidants scavengers SOD (1 /ig/ml), catalase (2 pg/ml) and methionine (0.25 mg/ml, to scavenge HOC1). In (b), neutrophils (1 x 106/ml) were suspended in buffer containing 75 jUM cytochrome c (to measure Of production) or 4 jUM scopoletin plus 5 /ig/ml horseradish peroxidase (to measure H202 production). In (c), neutrophils (2 x lOfyml) were placed in the chamber of a Clark-type 02 electrode. All measurements were made at 37 °C cell suspensions were stimulated by the addition of 1 /

Gold MH, Wariishi H,Valli K (1989) Extracellular peroxidases involved in lignin degradation by the white rot basidiomycete Phanerochaete chrysosporium. In Whitaker JR, Sonnet PE (eds) Biocatalysis in agricultural biotechnology. ACS symposium series 389. American Chemical Society, Washington, D.C., p 127 Thomas JA, Morris DR, Hager LP (1970) J Biol Chem 245 3135... 

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