Catalase iron properties

Typical examples of enzymes and their properties appear in the articles Copper Proteins Oxidases, Iron Heme Proteins, Peroxidases, Catalases Catalase-peroxidases Iron Heme... 

Oxoiron(IV) porphyrins, one oxidizing equivalent above the resting ferric state, are known as compound II in the catalytic cycle of peroxidases and catalases. The (Porp)Fe =0 complexes can be generated by (i) the homolytic O—O bond cleavage of (Porp)Fe -0-0-Fe (Porp), which is formed by the addition of dioxygen to iron(II) porphyrins in the presence of a nitrogen base, (ii) the chemical oxidation of iron(III) porphyrins by m-CPBA and PhIO under certain circumstances, (iii) the electrochemical oxidation of hydroxoiron(III) porphyrins, and (iv) the reactions of iron(III) porphyrins with hydroperoxides (ROOH) in aqueous or organic solvents. More detailed preparation methods and physical properties of various oxoiron(IV) porphyrin complexes are summarized in recent reviews. ... 

In the hemoproteins, the central ion is iron. In protoporphyrins, central ion and ligand form the heme. The same heme is inserted into different protein molecules, yielding different molecular complexes with different catalytic properties. For example, cytochromes facilitate electron transfer, catalase converts H2O2 into H2O, and hemoglobin stores and transports oxygen. The same chelates (central ion and ligand) can perform... 

It is well know that copper(II) labile complexes are most widely spread in nature as catalysts of oxidation-reduction reactions and in this sense probably they take second place after iron complexes. On the other hand, however, the copper chelate complexes do not act as catalysts of oxidation, but very often are among the most effective inhibitors of the oxidation reactions. The differences in their catalytic properties may be explained by the fact that all four coordination positions of the central ion are occupied by the chelate ligands. This was demonstrated by Siegel(l) by studying the catalase and peroxidase action of some copper chelate complexes (see scheme 1 in the next page). It was established that the above rate constants sharply decrease in the order I>>II>III of the following scheme and almost reach zero on coordination of the four ligand atoms. 

Trace metals, particularly copper, cobalt, and iron, greatly increase the rate of LO and influence the direction of peroxide decomposition [72], These metals function both to reduce the induction period and increase reaction rate by decomposing hydroperoxides. Trace levels of these catalysts, e.g., as little as 0.3 ppm iron or 0.01 ppm copper, will result in prooxidant effects [73]. Iron may exist in foods in the free form or as a part of an enzyme (contain organically bound haem, Fe+ or haemin, Fe+ ). Enzymes containing haematin compounds include catalase and peroxidase (plant tissues) and haemoglobin, myoglobin, and cytochrome C (animal tissues). While heat treatment results in denaturation of the enzymes, it frees the iron to greatly enhance its catalytic properties. This is particularly relevant in the formation of warmed-over off-flavor in cooked meats. 

The oxidase reaction is inhibited by carbon monoxide and by catalase, properties which are characteristic of oxidase-peroxidases, and which suggest that both ferrous iron and hydrogen peroxide participate in the overall reaction. If this is the case, inhibition by catalase may be explained by (1) destruction of hydrogen peroxide necessary to initiate the formation of ferroperoxidase, corresponding to the reduction of ferricatalase to ferrocatalase in the presence of peroxide and an electron donor (752), ) a side reaction in which oxyferroperoxidase is reduced to ferriperoxidase via Complex II (compare Fig. 17), or (S) destruction of peroxidase. In support of the last alternative, it has been observed that the decomposition of peroxide-... 

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