Peroxidases definitions

CAS 9003-99-0 EINECS/ELINCS 232-668-6 Synonyms Peroxidase Definition Enzyme obtained from milk Storage Sensitive to humidity keep under argon Uses Biological additive, stabilizer in cosmetics... 

The catalase-peroxidases present other challenges. More than 20 sequences are available, and interest in the enzyme arising from its involvement in the process of antihiotic sensitivity in tuherculosis-causing bacteria has resulted in a considerable body of kinetic and physiological information. Unfortunately, the determination of crystallization conditions and crystals remain an elusive goal, precluding the determination of a crystal structure. Furthermore, the presence of two possible reaction pathways, peroxidatic and catalatic, has complicated a definition of the reaction mechanisms and the identity of catalytic intermediates. There is work here to occupy biochemists for many more years. 

One of the difficulties of peroxidase studies is that the enzymes can react with a number of synthetic or natural substrates and that even the use of purified isozymes in assays for substrate specificity does not identify any definitive roles. A search for specific inhibitors represents another approach which is still poorly developed despite its potential utility. 

The exact disposition of the side chains in a globular protein is difficult to define in solution. Although it is likely that the peptide main chain (backbone) of the protein is relatively rigid, the side chains have been shown to be undergoing motion of several different types (see lysozyme, peroxidase, and carboxypeptidase). This means that the full definition of atomic positions in the structure requires a knowledge of the time dependence of their coordinates. The motion of side chains is likely to be different in the crystal and solution states, but this difference may well... 

Cytochrome oxidase (cytochrome aa3) represents the most important cytochrome of the a class. This is the terminal oxidase used in animals, plants, yeasts, algae and some bacteria. It contains two copper centres, giving four redox groups in total. This oxidase is discussed with other cytochromes that have a terminal oxidase function in Sections 62.1.12.4 and 62.1.12.5. These are cytochromes o, d and cd,. The oxidases fed719 and ax are not included in that discussion. The situation regarding cytochrome ax has been confused, partly due to uncertainty in the definition of this cytochrome. In some respects, the properties of cytochrome ax resemble those of mitochondrial and bacterial aa3. It functions as a terminal oxidase in some bacteria,720 but its role in E. coli is unknown. A soluble fraction from disrupted E. coli cells grown anaerobically on glycerol and fumarate contains a hemoprotein similar to cytochrome ax, which has catalase and peroxidase activity.721... 

To clarify the mechanism of reaction of P-450, it is crucial to characterize the reactive intermediates in the rate-determining step. Definitive evidence for an electron-transfer mechanism (C in Scheme 2) for the 7V-demethylation of N,N-dimethylanilines has been obtained by direct observation of the reduction of the high-valent species responsible for P-450 catalysis [96]. For peroxidase, an oxoferryl porphyrin 7r-radical cation, compound I ([(P)Fe =0] "), has been well characterized as the species equivalent to the proposed active intermediate of P-450 [97-103]. Compound I of horseradish peroxidase (HRP) can be readily generated by chemical oxidation of HRP [100-103]. The involvement of the electron-transfer process of compound I in the oxidation of several amines catalyzed by HRP was... 

I opics of continuing concern in Se nutrition include the availability of Se when supplied as selenomethionine or sodium selenite and the definition of normal levels of tissue selenium and the normal activity of GSH peroxidase. In many tissues, the Se asst>ciated with GSH peroxidase accounts for only a small proportion of tissue Sc, This situation raises the question of whether values of tissue Se or of enzyme activity can more accurately define adequate or optimal Se status. 

Schmid KW, Hittmair A, Schmidhammer H, et al. Non-deleterious inhibition of endogenous peroxidase activity (EPA) by cyclopropanone hydrate A definitive approach. J Histochem Cytochem. 1989 37 473. 

The conversion of the green primary complex into the pale red secondary complex appears to be a reduction process even though it occurs in the absence of any added hydrogen donors. The most definite evidence for this is the case of peroxidase where the speed of the conversion is increased in the presence of all compounds with which the peroxide system reacts (Chance, 55). For catalase, where the conversion can only be obtained with alkyl hydroperoxides, the evidence is not so clear-cut, but at least the velocity of formation of the secondary complexes increases as the hydroperoxide concentration is increased. An alternative explanation for these effects would be that the primary and secondary complexes are in some sort of equilibrium where removal of the latter would have the effect of increasing the rate of conversion. There is no indication of any such equilibrium, however, and direct reduction of the primary complex appears to be the most likely explanation. One possible formulation for this change involves the production of a ferryl ion type of compound by the removal of an OH radical by the hydrogen donor from the 02H anion bound to the iron atom ... 

An example of a calculation of the Lyapunov exponents and dimension, for a simple four-variable model of the peroxidase-oxidase reaction will help to clarify these general definitions. The following material is adapted from the presentation in Ref. 94. As described earlier, the Lyapunov dimension and the correlation dimension, D, serve as upper and lower bounds, respectively, to the fractal dimension of the strange attractor. The simple four-variable model is similar to the Degn—Olsen-Ferram (DOP) model discussed in a previous section but was suggested by L. F. Olsen a few years after the DOP model was introduced. It remains the simplest model the peroxidase-oxidase reaction which is consistent with the most experimental observations about this reaction. The rate equations for this model are ... 

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