Iron protoporphyrin IX and

Microperoxidase-11, MP-11, heme-undecapeptide, prepared by pepsin digestion of cytochrome c, retains the proximal His ligand and two thioether bonds between iron-protoporphyrin IX and two Cys residues. The peroxidase activities of MPs have been demonstrated in the oxidation of so-called peroxidase s substrates, phenolic compounds, in the presence of H2O2. MPs are unique and simple hemoprotein which are not restricted by consideration of the apoprotein structure. In this study, cytochrome P-450-hke reactivities of MP-11, sulfide oxidation, N-dealkylation, and olefin epoxidation, were... 

Cytochromes were first named and classified on the basis of their absorption spectra (Figure 21.9), which depend upon the structure and environment of their heme groups. The b cytochromes contain iron—protoporphyrin IX (Figure 21.10), the same heme found in hemoglobin and myoglobin. The c cytochromes contain heme c, derived from iron-protoporphyrin IX by the covalent attachment of cysteine residues from the associated protein. UQ-cyt c... 

FIGURE 21.10 The structures of iron protoporphyrin IX, heme c, and heme a. 

IX is accompanied by its transport back into the mitochondria whence it came, to undergo oxidation of its methylene groups to protoporphyrin IX and insertion of iron to yield the end product, haem. The two major sites of haem biosynthesis are erythroid cells, which synthesize around 85 % of the body s haem groups, and the liver, which synthesizes most of the remainder. A major function of haem in liver is as the prosthetic group of cytochrome P450, the importance of which in detoxification has been discussed in Chapter 2. The liver cell must synthesize cytochrome P450 throughout its lifetime in quantities that vary with conditions. In contrast, the... 

The second ligninolytic enzyme, MnP, has been identified (U), purified and characterized (13-16). MnP is an H O -dependent heme glycoprotein (M -46,000) with an iron protoporphyrin iX prosthetic group. MnP catalyzes the Mn -dependent oxidation of a variety of phenols and phenolic lignin model compounds (6,8.13-15,17). Electronic absorption... 

Scheme 3. Structures of hemin, the iron(III) complex of protoporphyrin IX, and recombinant HRP isoenzyme C (29).

The cytochromes P-450 monooxygenase system is actually a collection of isoenzymes, all of which possess an iron protoporphyrin IX as the prosthetic group. The monomer of the enzyme has a molecular weight of 45,000 to 55,000. The enzyme is membrane bound within the endoplasmic reticulum. Cytochromes P-450 are closely associated with another vital component of the system, NADPH cytochrome P-450 reductase. This is a flavoprotein, which has 1 mol of FAD and 1 mol of FMN per mol of apoprotein. The monomeric molecular weight of the enzyme is 78,000. The enzyme transfers two electrons to cytochromes P-450, but one at a time. There only seems to be one reductase, which serves a group of isoenzymes of cytochromes P-450, and consequently, its concentration is 1/10 to 1/30 that of cytochromes P-450. 

Heme is a complex of protoporphyrin IX and ferrous iron (Fe2+).The iron is held in the center of the heme molecule by bonds to the four nitrogens of the porphyrin ring. The Fe2+ can then form two additional bonds, including one to molecular oxygen. 

The porphyrin of heme is known as protoporphyrin IX, and the associated metal is iron [as Fe(II) or Fe(III)]. You will notice that the porphyrin ring carries methyl, ethenyl, and propanoic acid side chains ... 

Iron protoporphyrin IX (heme) is found in the b-type cytochromes and in hemoglobin and myoglobin. In heme c, cysteine residues of the protein (R) are attached covalently by thioether links to the two vinyl (—CH=CH2) groups of protoporphyrin IX. Heme c is found in the c cytochromes. In heme A, which is found in the a cytochromes, a 15-carbon isoprenoid side chain is attached to one of the vinyls, and a formyl group replaces one of the methyls. 

In 1989, BH4 was found to be a cofactor for nitric oxide synthase (NOS) [ 126, 127]. BH4 is also involved in dimerization of NOS, as NOS is catalytically active in a homodimer structure. Three isoforms of NOS exist neuronal NOS (NOS 1), inducible NOS (NOS 2) and endothelial NOS (NOS 3). BH4 is essential for all NOS isoforms. The NOS isoforms share approximately 50-60% sequence homology. Each NOS polypeptide is comprised of oxygenase and reductase domains. An N-terminal oxygenase domain contains iron protoporphyrin IX (heme), BH4 and an arginine binding site, and a C-terminal reductase domain contains flavin mononucleotide (FMN), and a reduced nicotin-amide adenine dinucleotide phosphate (NADPH) binding site. 

Figure 3 Formula of the hemes present in cytochromes a and b. Left iron-protoporphyrin IX of cytochromes b. Right heme of cytochromes a (C17H290 =...

Fig. 5.1 The structure of iron protoporphyrin IX, the prosthetic heme group of the peroxidases except where it is modified by the formation of covalent bonds to the methyl or vinyl groups. The a, (3-, y-, and 5-meso-carbon atoms, defined with respect to the pattern of the ring substituents, are labeled...

LiP has been purified to electrophoretic homogeneity by a combination of anion exchange chromatography and gel filtration (26-28). The enzyme is present as a series of Isozymes (28,29) with pi ranging from 3.2 to 4.0. LIP contains one mole of iron protoporphyrin IX per mole of enzyme and is a glycoprotein of molecular mass 41,000. 

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