Mechanism peroxidase

Sources and Biological Functions of Peroxidases Mechanisms of Peroxidase Catalysis. ... 

With tyrosinase, on the contrary, a two-electron oxidation occurs, as no EPR signal was detected in the catechol oxidation at pH 5.3 Melanins are polymerization products of tyrosine, whereby tyrosinase catalyses the first steps the formation of dopa (3,4-dihydroxyphenylalanine) and of dopaquinone, leading to an indolequi-none polymer The peroxidase mechanism for the conversion of tyrosine into dopa in melanogenesis was not substantiated In natural and synthetic melanins free radicals of a semiquinone type were detected by EPR 4-10 x 10 spins g of a hydrated suspension (the material was modified on drying and the number of free spins increased). The fairly symmetrical EPR signal had a g-value of 2.004 and a line-width of 4-10 G The melanins seem to be natural radical scavengers. 

Fig. 5.4 Schematic representation of the Poulos-Kraut peroxidase mechanism in which the conserved distal histidine serves as an acid-base catalyst that transfers a proton from the H202 to the terminal oxygen after formation of the [Fe(III)-OOH] intermediate. The proximal histidine iron ligand and the catalytic histidine and arginine are shown. In HRP, these residues are His 170,...

Fig. 4. A comparison of peroxidase, cytochrome c oxidase and cytochrome P-450 reaction mechanisms. Peroxidase mechanism adapted from that of Poulos[143], cytochrome P-450 mechanism adapted from that of Sligar [100], and cytochrome oxidase mechanism adapted from that of Babcock and Wikstrom[90]. RH, organic substrate for peroxidase and cytochrome P-450 (in the latter case the substrate is presumed to remain bound to the enzyme through most of the reaction cycle).

The mechanism shown below requires that Tyr385 first be oxidized to a radical. This reaction is achieved via the traditional peroxidase mechanism. 

Spectroscopic studies on di-heme peroxidases-mechanism of activation... 

Cytochrome c peroxidase is an enzyme which catalyses the oxidation of ferrocyto-chrome c by hydrogen peroxide. At low concentrations of ferrocytochrome c the catalysis follows the classical peroxidase mechanism developed for horseradish peroxidase (HRP) by Chance and George. Two oxidized cytochrome c peroxidase intermediates have been identified in the oxidation of ferrocytochrome c and ferro-cyanide, and (at low substrate concentrations) the reaction scheme is as shown in equation (7) (where CcP represents the native enzyme, CcP-I represents compound I... 

Figueroa-Espinoza, M. C. Rouau, X. (1998). Oxidative cross-linking of pentosans by a fungal laccase and a horseradish peroxidase mechanism of linkage between feruloylated arabinoxylans. Cereal Chemistry, 75, 259-265. 

An interesting difference from several of the oxidatic reactions previously described is the DPNHiOj stoichiometry of 2.0. This means that the DPN+ produced can be reduced back to the original form, and that the peroxidase mechanism could therefore perhaps provide a true respiratory system in some circumstances. 

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