Heme proteins horseradish peroxidase

A number of NO-derived reactive species can initiate lipid peroxidation, including nitrogen dioxide and, most notably, ONOO , which displays unique properties as a mediator of lipid oxidation. On a molecular basis, ONOO is a more potent lipid oxidant than hydrogen peroxide and, unlike H2O2, it does not require metal catalysis. The one-electron oxidants such as metals, as well as heme proteins and peroxynitrite, are assumed to play an important role in many diseases associated with oxidative stress. Heme proteins such as horseradish peroxidase (HRP) can produce alkylperoxyl radicals through two sequential... 

The pertinent epithelia tissues of the oral cavity are the buccal and the sublingual ones. They are nonkeratinized tissues, both covered with a thin layer of mucus (Figure 1.8). The first is 500-800 pm thick, whereas the latter is 100-200 pm thick, and more vascularized than the former [121,122]. This difference in thickness may be a possible cause for the diversity in their permeabilities the sublingual is more permeable than the buccal mucosa, and the palatal mucosa is the least permeable. Permeability values of water and horseradish peroxidase (a 40-kDa heme protein commonly used as a permeation label) in the pig oral cavity are shown in Table 1.2. Blood vasculature in both epithelia of the oral cavity does not drain directly to... 

The peroxidase activity of PGHS is comparable to that of better known peroxidases such as horseradish peroxidase (HRP). The catalytic cycle of HRP is shown in Figure 5 [9], Its first step is the formation of an intermediate very often found in hemoproteins by transfer of an oxygen atom from various oxygen atom donors to the Fe(III) heme (Eq. 6). It is a high-valent iron-oxo species, at least formally a Fe(V)=0 complex. In fact, the detailed electronic structure of this intermediate depends on the environment of the heme provided by the protein. In HRP, this intermediate (called compound I) is a (porphyrin radical-cation)-Fe(IV)=0 complex, as shown by many spectroscopic techniques [9],... 

Although ferryl intermediates of horseradish peroxidase and microperoxidase-8 have been produced in reactions with photogenerated [Ru(bpy)3]3+ [5], analogous experiments with P450s were unsuccessful, presumably due to the inefficiency of electron transfer from the buried heme active site through the protein backbone [6]. Photoactive molecular wires (sometimes referred to as metal-diimine wires, sensitizer-tethered substrates, or electron tunneling wires) were developed to circumvent this problem by providing a direct ET pathway between [Ru(bpy)3]3+ and the heme. These molecular wires, which combine the excellent photophysical properties of metal-diimine complexes... 

Ator MA, Ortiz de Montellano PR. Protein control of prosthetic heme reactivity reaction of substrates with the heme edge of horseradish peroxidase. J Biol Chem 1987 262(4) 1542-1551. 

Another class of heme proteins containing iron protoporphyrin as the active center includes enzymes such as cytochrome P-450 and horseradish peroxidase (HRP). The former is a monooxygenase enzyme (MW 50,000) that catalyzes hydroxylation reaction of substrates such as drugs, steroids and carcinogens ... 

Huang LS, Wojciechowski G, Ortiz de Montellano PR (2006) Role of heme-protein covalent bonds in mammalian peroxidases - Protection of the heme by a single engineered heme-protein link in horseradish peroxidase. J Biol Chem 281 18983-18988... 

Fig. 4.1 Relation between redox potential of Fe(III)/Fe(II) and Compound II/Fe(III) couples of heme peroxidases. Values were taken from Tables 4.3 and 4.4 for the following proteins soybean peroxidase, horseradish peroxidase, cytochrome c peroxidase, C. cinereus peroxidase, lactoper-oxidase, manganese peroxidase...

Colas C, Ortiz de Montellano PR (2004) Horseradish peroxidase mutants that autocataly-tically modify their prosthetic heme group. Insights into mammalian peroxidase heme-protein covalent bonds. J Biol Chem 279 24131-24140... 

Electronic absorption maxima for LIP, MnP, horseradish peroxidase (HRP) and various llganded forms of these enzymes are shown in Table I. The spectra of native LIP and MnP are characteristic of high-spin ferric heme proteins, with Soret and visible maxima ( 407, 502 and... 

One of the variables in the structures of the porphyrins present in heme proteins is the presence or absence of vinyl substituents on the periphery of the macrocycle. For example, b hemes have vinyl substituents whereas c hemes do not. Because of the sensitivity of such vinyl substituents during synthetic transformations, it has often been desirable to use octa-alkyl porphyrins in model studies of the spectroscopic properties of heme systems. The development of improved methods for the preparation of octa-alkyl porphyrins has likewise increased the availability of such porphyrins for model studies (20, 21). To assess the effect that replacement of the two vinyl substituents in protoporphyrin IX with alkyl (ethyl) groups has on the MCD properties of the heme system, an extensive and systematic study of the MCD properties of mesoheme IX-reconstituted myoglobin and horseradish peroxidase in comparison with the spectra of the native protoheme-bound proteins has been carried out (22). The structures of these two porphyrins are shown in Figure 3. 

Myoglobin has the same prosthetic group as some peroxidases, such as horseradish peroxidase (HRP) or cytochrome c peroxidase, and reacts with H2O2 to produce a ferryl species, PFe(IV)=0, observed in the native peroxidase (see Iron Heme Proteins, Peroxidases, Catalases Catalase-peroxidases). However, the catalytic activity of myoglobin toward substrate oxidation is very low, because... 

Cytochrome P-450, which is the most extensively studied of the monooxygenase proteins, has a heme-iron active center with an axial thiol ligand (a cysteine residue). However, most chemical model investigations use simple iron(III) porphyrins without thiolate ligands. As a result, model mechanisms for cytochrome P-450 invoke a reactive intermediate that is formulated to be equivalent to Compound I of horseradish peroxidase, (por+-)Fe =0, with a high-potential porphyrin cation radical. Such a species would be reduced by thiolate, and therefore is an unreasonable formulation for the reactive center of cytochrome P-450. 

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