Horseradish peroxidase compound

Rodrfguez-Lopez, J.N., Gilabert, M.A., Tudela, J., Thorneley, R.N.R, and Garcfa-Canovas, R, Reactivity of horseradish peroxidase compound II toward substrates kinetic evidence for a two-step mechanism,... 

Figure 5. Comparison of the optical absorption spectra of cobalt(III) porphyrin ir-cation radical species with those of catalase compound / and horseradish peroxidase compound L The ground states of the bromide and perchlorate species are 2A lu and 2Agu, respectively.

The rate constants of kn and kx obtained using Eq. (24) reveal that (i) the activity of Fem-TAMLs in bleaching Safranine O (k ) increases more than 10-fold when the tail ethyl groups of la are replaced by fluorine atoms in lk. The rate constant kn for lk equals l(rM 1s 1 at 25°C, a value that corresponds to those found for the reactivity of horseradish peroxidase Compound II... 

The form of the enzyme with the greatest oxidation potential is known as horseradish peroxidase, compound 1 (HRP-I), which consists of a radical cation stabilized throughout the highly conjugated protoporphyrin IX ring system. In the presence of vindoline, HRP-I is reduced to HRP-H, an Fe(IV) form of the enzyme. The vindoline cation radical 55 thus formed eliminates a second elec-... 

HOPhjSil O, 42 214 Horseradish peroxidase compound I formation, 43 97-98 endogenous reduction of intermediates, 43 100... 

Baek HK, Van Wart HE (1989) Elementary steps in the formation of horseradish peroxidase Compound I Direct observation of Compound 0, a new intermediate with a hyperporphyrin spectrum. Biochemistry 28 5714-5719... 

Rutter R, Valentine M, Hendrich MP et al (1983) Chemical nature of the porphyrin 7i cation radical in horseradish peroxidase Compound I. Biochemistry 22 4769—4774... 

Roberts JE, Hoffman BM, Rutter R et al (1981) Electron double resonance of horseradish peroxidase Compound I. Detection of the porphyrin 7i-cation radical. J Biol Chem 256 2118-2121... 

Job D, Dunford HB (1976) Substituent effect on the oxidation of phenols and aromatic amines by horseradish peroxidase Compound I. Eur J Biochem 66 607-614... 

Dunford HB, Adeniran AJ (1986) Hammett op correlation for reactions of horseradish peroxidase Compound II with phenols. Arch Biochem Biophys 251 536—542... 

Sakurada J, Sckiguchi R, Sato Ket al (1990) Kinetic and molecular orbital studies on the rate of oxidation of monosubstituted phenols and anilines by horseradish peroxidase Compound II. Biochemistry 29 4093 1098... 

Suh YJ, Hager LP (1991) Chemical and transient state kinetic studies on the formation and decomposition of horseradish peroxidase compounds Xj and Xn. J Biol Chem 266 22102-22109... 

Sitter AJ, Reczek CM, Temer J (1986) Comparison of the heme structures of horseradish peroxidase compounds X and II by resonance Raman spectroscopy. J Biol Chem 261 8638-8642... 

Zimmer J, Van Wart HE (1982) Resonance Raman spectrum of horseradish peroxidase compound III comparison with oxyhemoglobin. Biochem Biophys Res Commun 108 977-981... 

Filizola, M. and Loew, G.H. (2000) Role of protein environment in horseradish peroxidase compound I formation molecular dynamic stimulation of horseradish peroxidase-HOOH complex, J. Am. Chem. Soc. 122,18-25. 

MCD spectra perhaps provide the best fingerprint for the existence of an FeIV=0 structure. Fig. 8 shows that there is a great similarity between the spectra of horseradish peroxidase compound II, horseradish peroxidase compound X, cytochrome c peroxidase compound I, Pseudomonas aeruginosa peroxidase compound I and ferryl myoglobin at acid pH. Similar features are seen in the spectra of catalase [170] and myoglobin [171] compound II. 

The reasons for the difference between the spectra of ferryl myoglobin at acid and alkaline pH are not clear. However, it has been suggested that deprotonation of the proximal histidine ligand at alkaline pH may be responsible [175,176], Furthermore a third form of ferryl iron was detected in varying amounts in preparations of horseradish peroxidase compound II, ferryl myoglobin and cytochrome c peroxidase compound I [162], To account for these spectra it was proposed that the iron-histidine bond was broken, leaving a five-coordinate ferryl haem. 

Mossbauer spectra has been extensively used to probe the structure of the iron nucleus in biological FeIV=0 compounds. These include horseradish peroxidase compoundl[134,180,181], horseradish peroxidase compound II [182,183], horseradish peroxidase compound X [181], Japanese-radish peroxidase compounds I and II [184], chloroperoxidase compound I [185], cytochrome c peroxidase compound I [186] and ferryl myoglobin [183]. Examples of Mossbauer spectra attributed to non-porphyrin-bound FeIV are only available from synthetic model compounds. These include compounds with [130] and without [4-8] an FeIV=0 bond. 

Unlike the case of optical or MCD spectroscopy, the presence of a nearby free radical (porphyrin or amino acid) has only a small effect on the Mossbauer spectra of ferryl iron (by contrast the nature of the axial ligand appears to have a greater effect on the Mossbauer spectra). Thus in the absence of a magnetic field there is little difference between the Mossbauer spectra of horseradish peroxidase compounds I and II [134,181,183]. Due to... 

Fig 17. MCD spectra recorded at 5 T and at 50 or 100 K of Fe(IV)(por) in various protein environments HRPCII, horseradish peroxidase compound II HRPCX, horseradish peroxidase compound X YCCP, yeast cytochrome c peroxidase compound ES PsCCP, compound I of the diheme cytochrome c peroxidase Mb pH 3.5, the ferryl form of myoglobin formed at pH 3.5 Mb pD 9.0, the same compound found at pD 9.0. 

Both oxidizing equivalents of the hydroperoxide are incorporated into compound I, through an oxygen-atom transfer process ". A free radical is generated elsewhere in the molecule on amino acid residue(s) in the case of yeast cytochrome c peroxidase" and at a site strongly coupled to the iron in horseradish peroxidase . (Compound I of yeast cytochrome c peroxidase is called complex ES in earlier literature.) EPR results on horseradish peroxidase are interpreted in terms of a porphyrin rr-cation radical for compound I . Thus, EPR data prove that one oxidizing equivalent obtained from the hydroperoxide is a free radical species"" ... 

Although the precise mechanism for the enhancement remains unknown, Thorpe and Kricka (T8) have proposed that enhancers render the sequence of events for unenhanced luminol oxidation (see Section 3.1.3) more efficient. This would be consistent with kinetic studies on the reactivity of phenol enhancers with the horseradish peroxidase intermediates Compounds I and II (Hll, VIO). Specifically, the hypothesis is that (a) horseradish peroxidase Compounds I and II... 

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