Ferric protoporphyrin

Peroxidases (E.C. 1.11.1.7) are ubiquitously found in plants, microorganisms and animals. They are either named after their sources, for example, horseradish peroxidase and lacto- or myeloperoxidase, or akin to their substrates, such as cytochrome c, chloro- or lignin peroxidases. Most of the peroxidases studied so far are heme enzymes with ferric protoporphyrin IX (protoheme) as the prosthetic group (Fig. 1). However, the active centers of some peroxidases also contain selenium (glutathione peroxidase) [7], vanadium (bromoperoxidase)... 

Heme-dependent monooxygenases contain ferric protoporphyrin IX, the heme, as the cofactor and protect us from the xenobiotics, toxins, food, and chemicals we take up. As these proteins exhibit a very strong absorption band maximum at... 

The molecular weight of cytochrome c peroxidase has been determined to be 34,100 on the basis of a sedimentation constant of 3.55 S, a diffusion constant of 9.44 F, and a partial specific volume of 0.733 ml/g (4 )-The enzyme exists as a monodisperse monomer containing one ferric protoporphyrin IX, which is noncovalently bound (/, , 14). No other transition metal is detected in crystalline preparations of the enzyme (22). The apoenzyme moiety is an acidic protein with an isoelectric point at pH... 

All the remaining questions focus on comparisons of CCP, MMB, and CAT. The first question addressed is Can the differences in the active site of CCP, MMB, and CAT account for the differences in their observed electromagnetic properties MMB and CCP (55, 56) have been found to have the same heme unit, a ferric protoporphyrin-IX with a water and an imidazole as axial ligands. CAT has a single... 

Typically, all carefully characterized catalases are oligomers (isoelectric point 5.5) containing four (43-46) tetrahedrally arranged (47), 60,000-dalton subunits (48-60). Each subunit consists of a single polypeptide chain (41) that associates with a single prosthetic group, ferric protoporphyrin IX (61). The subunits apparently function independently of one another (62, 63). 

Figure 16.2-34. Ferric protoporphyrin IX as prosthetic group in most peroxidases.

The generation of reactive catalase in its oxidized stage can also be achieved by direct electrochemical oxidation (transfer of electrons from ferric protoporphyrin IX to the electrode). Thus, catalase immobilized on graphite electrodes has been used for the hydrogen peroxide-free oxidation of phenol [168l... 

In the editorial preface to the first volume of Advances in Catalysis the decision was made known not to publish reviews of specialized topics in biocatalysis but from time to time to bring reports in which the relationship and parallelism between this special field and normal catalysis are discussed. This is the first of these reports. Its purpose is to examine the reactions of four hemoproteins, hemoglobin, myoglobin, peroxidase, and catalase, which all contain the same coordination compound of iron—ferrous or ferric protoporphyrin attached to different protein molecules, with oxygen, hydrogen peroxide, and in a few cases additional reducing substances. Some of these reactions are specific ... 

Four of the six valencies of the central iron atom are held in the planar porphyrin ring, and when heme and hematin are in true solution the fifth and sixth bonds completing an octahedral complex are assumed to be occupied by water molecules. These compounds, i.e., heme and hemin, can be represented as H2OFepH20 and H2()Fe,+TI20, where Fep and Fep+ represent ferrous and ferric protoporphyrin respectively. Ionization of one of the water molecules attached to heme in solution... 

Baron " and by Clark " in their studies on the potentials of the hemo-chromogens. The hemochromogens are thermodynamically reversible univalent redox systems, that is, they require a negligible activation energy to accept an electron in the oxidized state and to release an electron in the reduced state. The redox level of the iron in the heme may be varied by varying the N compounds that complex with the heme, and one may obtain E, values at pH 7 (Table III) as negative as —0.183 in the case of the ferrous-ferric protoporphyrin.2CN system and as high as... 

Most peroxidases are heme enzymes and contain the ferric protoporphyrin IX (protoheme) group with an iron atom in their active center (Fig. 1). Only a few other peroxidases known so far have other metal centers and/or different prosthetic groups. Glutathione peroxidase, for example, has a selen-... 

The reaction of ferric protoporphyrin IX with cyanide, and its reaction with imidazole, are assigned associative mechanisms on the basis of their activation volumes. However, it is not entirely clear what assumptions are involved in relation to solvation and the partial molar volumes of the incoming groups. ... 

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