Proteins heme-containing

HEMOPROTEINS. These proteins are actually a subclass of metalloproteins because their prosthetic group is heme, the name given to iron protoporphyrin IX (Figure 5.15). Because heme-containing proteins enjoy so many prominent biological functions, they are considered a class by themselves. 

Mammalian sulfite oxidase is the last enzyme in the pathway for degradation of sulfur-containing amino acids. Sulfite oxidase (SO) catalyzes the oxidation of sulfite (SO ) to sulfate (S04 ), using the heme-containing protein, cytochrome c, as electron acceptor ... 

In addition to intracellular heme-containing proteins, big-conductance calcium-dependent K+ (BKCa) channels and calcium-spark activated transient Kca channels in plasma membrane are also tar geted by CO [3]. As well known, nitric oxide (NO) also activates BKca channels in vascular smooth muscle cells. While both NO and CO open BKCa channels, CO mainly acts on alpha subunit of BKCa channels and NO mainly acts on beta subunit of BKca channels in vascular smooth muscle cells. Rather than a redundant machinery, CO and NO provide a coordinated regulation of BKca channel function by acting on different subunits of the same protein complex. Furthermore, pretreatment of vascular smooth muscle... 

Cytochrome c is a heme containing protein which occurs in muscle at lower concentrations than does myoglobin. It was demonstrated some time ago (18) that oxidized cytochrome c reacts with gaseous nitrite oxide to produce a nltrosyl compound. Recent work (19, 20, 21) has examined the reactions of cytochrome c with nitrite and the contribution of the product formed to cured meat color in considerably more detail. The general conclusion is that even at the pH normally encountered in meat, the reaction can take place in the presence of ascorbic acid but probably does not affect meat color because of the unstable nature of the reaction product and the low concentration. 

Hemoglobin is another heme-containing protein, which has been shown to be active towards PAH, oxidation in presence of peroxide [420], This protein was also modified via PEG and methyl esterification to obtain a more hydrophobic protein with altered activity and substrate specificity. The modified protein had four times the catalytic efficiency than that of the unmodified protein for pyrene oxidation. Several PAHs were also oxidized including acenaphthene, anthracene, azulene, benzo(a)pyrene, fluoranthene, fluorene, and phenanthrene however, no reaction was observed with chrysene and biphenyl. Modification of hemoglobin with p-nitrophenol and p-aminophenol has also been reported [425], The modification was reported to enhance the substrate affinity up to 30 times. Additionally, the solvent concentration at which the enzyme showed maximum activity was also higher. Both the effects were attributed to the increase in hydrophobicity of the active site. 

Myeloperoxidase (MPO) is a heme containing protein that catalyzes the two electron oxidation of halides (Cl-, Br- and I-) and pseudohalide (SCN-) to the corresponding hypohalous acid (Eq. (51)) in a process that is dependent upon [X-], [H202] and [H+] (135). MPO is found in high concentrations in neutrophiles and plays important roles in immune response and inflammation (136). 

Hydroxy- urea Hydroxamic acid if HjN NH 1 OH OH H H202/CuZn-S0D or ceruloplasimin, H202/Cu2+, heme-containing proteins Peroxidase Guanylate cyclase... 

Myoglobin in many respects is the prototypical example of the larger family of heme containing proteins and enzymes that vary in function from the relatively simple process of reversible binding of an electron to the activation of dioxygen for substrate hydroxylation. The relationship between members of this family of proteins is not based simply on structural similarities but on similarities in chemical reactivity as well. As the structure of myoglobin is relatively simple compared to other heme proteins and as it was the first for which the three-dimensional... 

Heme alone can reportedly elicit a catalatic reaction (the reaction mediated by catalase) but at a much reduced, almost negligible, rate compared to the catalatic proteins containing heme, and this may explain the observation of catalase activity in enzymes not normally associated with catalatic activity (4, 5). Other enz5unes have evolved that can catalyze a similar reaction in the absence of heme, but this review will limit itself to a consideration of heme containing proteins with catalatic activity. 

Several heme-containing proteins, including most peroxidases 12), have been observed to exhibit a low level of catalatic activity, with the chloroperoxidase from Caldariomyces fumago exhibiting the greatest reactivity as a catalase (13-15). Despite the fact that there is as yet only one such example to consider, it provides an alternate mechanism for the catalatic reaction and is addressed in this review. It was first characterized for its ability to chlorinate organic substrates in the presence of chloride and hydrogen peroxide at acid pH, but was later found... 

Other proteins such as methemoglobin and metmyoglobin have been observed to produce molecular oxygen in the presence of hydrogen peroxide, but at a very low rate (5). This may simply be a property of the heme, which can promote a low-level catalatic reaction in the absence of protein. Consequently, it is possible that all heme-containing proteins may exhibit catalatic reactions if assayed carefully, but such minor, largely nonquantifiable activities are not considered here. 

Heme coenzymes (8) with redox functions exist in the respiratory chain (see p. 140), in photosynthesis (see p. 128), and in monooxygenases and peroxidases (see p. 24). Heme-containing proteins with redox functions are also referred to as cytochromes. In cytochromes, in contrast to hemoglobin and myoglobin, the iron changes its valence (usually between +2 and +3). There are several classes of heme (a, b, and c), which have different types of substituent - Ri to - R 3. Hemoglobin, myoglobin, and the heme enzymes contain heme b. Two types of heme a are found in cytochrome c oxidase (see p. 132), while heme c mainly occurs in cytochrome c, where it is covalently bound with cysteine residues of the protein part via thioester bonds. 

Carboxylic groups of the protoporphyrin IX ligand (Scheme 10) are phenomenal candidates for the targeted active-site modification of HRP and other heme-containing proteins. There is a clear parallel with the active site modification of GO (Section IV.A.2). The modification of hemin chloride by H2NCH2Fc in the presence of EDC and V-hydroxysuccinimide in DMF affording mono- and bis-amidated propionic acid residues is shown in Scheme 10 (144). The Fc Heme is actually a mixture of two diastereomers. -HRP has been prepared according to an acidic methyl ethyl ketone procedure of Teale (145)... 

Heme containing proteins are also involved in nitrite reduction. Cytochrome... 

Like hemerythrin, hemocyanin is an oxygen transport non-heme-containing protein found in some arthropods and molluscs (104,105). In the 02-bound form, hemocyanin contains an antiferromagnetically coupled binuclear copper(II) system (106) ligated by histidine residues, with a sideways / 2-v2 V2 peroxo group bound to both Cu11 centers (104), which superseded the previous model (107). 

Frataxin is another protein which was shown to be targeted into hydrogenosomes (Dolezal et al. 2007). Importantly, I vaginalis frataxin can, in part, functionally replace mitochondrial frataxin, as demonstrated by its ability to partially restore defects in FeS cluster assembly in Saccharomyces cerevisiae Ayfhl mutants and frataxin-deficient Trypanosoma brucei (our unpublished data). In yeast, I vaginalis frataxin also partially restored defects in heme synthesis, although neither heme-containing proteins nor components involved in heme synthesis have been identified in T. vaginalis (Dolezal et al. 2007). 

In free heme molecules (heme not bound to protein), reaction of oxygen at one of the two open coordination bonds of iron (perpendicular to the plane of the porphyrin molecule, above and below) can result in irreversible conversion of Fe2+ to Fes+. In heme-containing proteins, this reaction is prevented by sequestering of the heme deep within the protein structure where access to the two open coordination bonds is restricted. One of these two coordination bonds is occupied by a side-chain nitrogen of a His residue. The... 

Myoglobin is a heme protein found in the skeletal muscle of meat-producing animals. It provides the red color associated with meat and thus affects the appearance of meat. Two other heme-containing proteins found in meat are hemoglobin and cytochromes. These are generally present at relatively low concentrations and are not considered to substantially impact the color of meat from normal animals (Warriss and Rhodes, 1977 Ledward, 1984). Several reviews have been published on the biochemistry of myoglobin and its relevance in meat (Faustman and Cassens, 1990 Renerre, 1990 Cornforth, 1994). 

The electron carriers that participate in the flow of electrons to 02 are a structurally diverse group. Occupying a central position are a series of heme-containing proteins, the cytochromes. Hemes are porphyrins with iron at the center (see chapter 10). Three main types of cytochromes, a, b, and c, exist and are distinguished by different substituents on the periphery of the porphyrin ring and different modes of attachment of the porphyrin to the protein (fig. 14.3). Cytochrome c is a small, water-soluble protein associated loosely with the inner mitochondrial membrane. Another c cytochrome (c,), two b cytochromes (bL and bH), and two a cytochromes (a and a3) are embedded in the membrane as parts of large complexes described below. 

Cytochromes. Heme-containing proteins that function as electron carriers in oxidative phosphorylation and photosynthesis. 

Besides low spin ferric heme containing proteins [102,103], four- [104] and five-coordinated [105] high spin cobalt(II)-containing proteins have been studied. Lanthanides have been used from the early times of NMR of paramagnetic molecules [106-108]. 

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