Peroxidase microperoxidases

Chemiluminescence and bioluminescence are also used in immunoassays to detect conventional enzyme labels (eg, alkaline phosphatase, P-galactosidase, glucose oxidase, glucose 6-phosphate dehydrogenase, horseradish peroxidase, microperoxidase, xanthine oxidase). The enhanced chemiluminescence assay for horseradish peroxidase (luminol-peroxide-4-iodophenol detection reagent) and various chemiluminescence adamantyl 1,2-dioxetane aryl phosphate substrates, eg, (11) and (15) for alkaline phosphatase labels are in routine use in immunoassay analyzers and in Western blotting kits (261—266). 

Direct electron transfer has also been achieved with many metalloproteins such as cytochrome C, horseradish peroxidase, microperoxidase (MP-11), myoglobin, hemoglobin, catalase, azurin, and so on, immobilized on different CNT-modified electrodes [45, 61, 144—153]. 

The oxidation of iodide is performed by enzymes of the peroxidase type (Morrison, 1980), mainly lactoperoxidase, but also by horseradish peroxidase, microperoxidase and chloroperoxidase, which are hemoproteins with tetrapyr-rolic cores chelating iron. These enzymes are active in the presence of small amounts of hydrogen peroxide or glucose oxidase. They form a first complex with H2O2 that... 

Tanaka, T. and Sakano, A. (1985) Differences in permeability of microperoxidase and horseradish peroxidase into alveolar bone of developing rats. Journal of Dental Research 64 870-876... 

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... 

Laszlo JA, Compton DL (2002) Comparison of peroxidase activities of hemin, cytochrome c and microperoxidase-11 in molecular solvents and imidazolium-based ionic liquids. J Mol Catal B Enzym 18 109-120... 

Casella L, De Gioia L, Frontoso Silvestri G (2000) Covalently modified microperoxidases as heme-peptide models for peroxidases. J Inorg Biochem 79 31 -0... 

Several enzymes with peroxidase-like action have also been used in immunoassays. Microperoxidases are catalytically active fragments obtained from cytochrome c by proteolytic action. They consist of the heme group covalently coupled to a short peptide alpha helix (26). The active site structure is similar to that of peroxidase Four of the six possible coordination bonds of the iron atom are occupied by bonding to the porphyrin while the fifth complexes with a histidine residue and the sixth is exposed to the environment and forms the catalytically active portion of the molecule. The reaction mechanism and spectrum of substrates is similar to HRP, although the specific activity is variable... 

As in the case of horseradish peroxidase, several synthetic metalloporphyrins in the presence of H2O2 have been found to be potent catalysts for the chemiluminescent oxidation of luminol or isoluminol. The microperoxidases, mainly MP8 and MPll, have been shown to act as functional peroxidase enzyme models. " However, they are readily inactivated within one min of catalytic turnover, and incorporation into a molecular sieve... 

The reaction of peroxide with ferrous heme iron is the basis of electrocatalytic peroxide sensors. A selection that gives a representative overview of the biomolecules and transducers is included in Table 2.5. Peroxidase, catalase, haemoglobin, cytochrome c, microperoxidase and hemin can all be explored for peroxide measurement. Most papers on DET-based biosensor are related to peroxide detection in a variety of environments with peroxidases. 

Microperoxidase is the heme-containing peptide portion of Cyt c that retains peroxidase activity. Several microperoxidases are available with different numbers of amino acid residues. The conformation of microperoxidase-11 (the microperoxidase with 11 amino acids in the peptide) adsorbed on roughened Ag electrodes was studied using Fourier transform SERS and shown to be adsorbed via the a-helical polypeptide chain [299]. As expected the characteristic amide 1 and 111 bands for the protein backbone were the strongest. Similarly microperoxidase-8 was studied by combined SERRS and electrochemistry where it was shown that the heme existed in the penta-coordinated state and could bind cyanide as the sixth ligand [300]. 

Comparative activities of microperoxidases, peroxidase (C) and cytochrome c at their optimum pH and with diaminobenzidine as hydrogen donor... 

Data compiled from Plattner et al. (1977) and Tiggeman et al. (1981) have been normalized to reflect relative activities. Both studies reported the activity for MPOase(9), which is, therefore, taken as a reference. However, the activity of MPOase(9) is probably somewhat too high since it is based on pure material (i.e., without residual water or salt) as calculated from amino acid analysis, whereas the other data were obtained for weighed samples. MPOase(8), (9), and (11) correspond to microperoxidase with 8, 9, and 11 amino acids, respectively POase is horseradish peroxidase. 

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