By horseradish peroxidase

Martmez-Parra, J. and Munoz, R., An approach to the characterization of betanine oxidation catalyzed by horseradish peroxidase, J. Agric. Food Chem., 45, 2984, 1997. 

Martmez-Parra, J. and Munoz, R., An approach to the characterization of betanine oxidation catalyzed by horseradish peroxidase, J. Agric. Food Chem., 45, 2984, 1997. Martmez-Parra, J. and Munoz, R., Characterization of betacyanin oxidation catalyzed by a peroxidase from Beta vulgaris L. roots, J. Agric. Food Chem., 49, 4064, 2001. Ashie, l.N.A. Simpson, B.K., and Smith, J.P., Mechanisms for controlling enzymatic reactions in foods, Crit. Rev. Food Sci. Nutr., 36, 1, 1996. 

Choi, Y.J., Chae, H.J., and Kim, E.Y., Steady-state oxidation model by horseradish peroxidase for the estimation of the non-inactivation zone in the enzymatic removal of pentachlorophenol, J. Biosci. Bioeng., 88, 368-373, 1999. 

Zhang, G. and Nicell, J.A., Treatment of aqueous pentachlorophenol by horseradish peroxidase and hydrogen peroxide, Water Res., 34, 1629-1637, 2000. 

Extensive studies have established that the catalytic cycle for the reduction of hydroperoxides by horseradish peroxidase is the one depicted in Figure 6 (38). The resting enzyme interacts with the peroxide to form an enzyme-substrate complex that decomposes to alcohol and an iron-oxo complex that is two oxidizing equivalents above the resting state of the enzyme. For catalytic turnover to occur the iron-oxo complex must be reduced. The two electrons are furnished by reducing substrates either by electron transfer from substrate to enzyme or by oxygen transfer from enzyme to substrate. Substrate oxidation by the iron-oxo complex supports continuous hydroperoxide reduction. When either reducing substrate or hydroperoxide is exhausted, the catalytic cycle stops. 

HTAC cationic micelles also markedly enhance the CL intensity of fluorescein (FL) in the oxidation of hydrogen peroxide catalyzed by horseradish peroxidase (HRP) [39], However, no CL enhancement was observed when anionic micelles of sodium dodecyl sulphate (SDS) or nonionic micelles of polyoxyethylene (23) dodecanol (Brij-35) were used (Fig. 9). CL enhancement is attributed to the electrostatic interaction of the anionic fluorescein with the HTAC micelles. The local concentration of fluorescein on the surface of the micelle increases the efficiency of the energy transferred from the singlet oxygen (which is produced in the peroxidation catalyzed by the HRP) to fluorescein. This chemiluminescent enhancement was applied to the determination of traces of hydrogen peroxide. The detection limit was three times smaller than that obtained in aqueous solution. 

Regeneration of superoxide during the oxidation of thiols hints at the possible prooxidant effect of these antioxidants. This suggestion was recently confirmed by Mottley and Mason [212] who have showed that superoxide was formed in the oxidation of DHLA by horseradish peroxidase in the presence of phenol. However, DHLA is dithiolic compound and the other mechanisms such as the concerted mechanism, which has been proposed earlier for flavonoids may be realized (Figure 29.6). 

Before the advent of enediyne antitumor antibiotics, there had been few examples of carbon radicals believed to mediate DNA cleavage. The simplest of all, the methyl radical has been shown to effect DNA cleavage under enzymatic as well as chemical conditions [24]. Oxidation of methylhydrazine by horseradish peroxidase or ferricyanide (Fig. 5) gave high yields of methyl radicals, which were shown to cleave DNA by purine ring alkylation. 

Scheme 4. Reduction of indicine lV-oxide catalyzed by horseradish peroxidase.

Scheme 17. The course of oxidation of vindoline by horseradish peroxidase.

Indicine IV-oxide (169) (Scheme 36) is a clinically important pyrrolizidine alkaloid being used in the treatment of neoplasms. The compound is an attractive drug candidate because it does not have the acute toxicity observed in other pyrrolizidine alkaloids. Indicine IV-oxide apparently demonstrates increased biological activity and toxicity after reduction to the tertiary amine. Duffel and Gillespie (90) demonstrated that horseradish peroxidase catalyzes the reduction of indicine IV-oxide to indicine in an anaerobic reaction requiring a reduced pyridine nucleotide (either NADH or NADPH) and a flavin coenzyme (FMN or FAD). Rat liver microsomes and the 100,000 x g supernatant fraction also catalyze the reduction of the IV-oxide, and cofactor requirements and inhibition characteristics with these enzyme systems are similar to those exhibited by horseradish peroxidase. Sodium azide inhibited the TV-oxide reduction reaction, while aminotriazole did not. With rat liver microsomes, IV-octylamine decreased... 

Shaffer CL, Morton MD, Hanzlik RP. N-dealkylation of an N-cyclopropylamine by horseradish peroxidase. Fate of the cyclopropyl group. J Am Chem Soc 2001 123(35) 8502-8508. 

When binding of the uncharged BP with DNA is catalyzed by horseradish peroxidase (Cavalieri et al. 1988b) or rat liver microsomes (Cavalieri et al. 1988a), the same pattern of the DNA-depurinating BP derivatives was obtained. As mentioned earlier, horseradish peroxidase activates BP by one-electron oxidation, hence, this result is just as expected (Rogan et al. 1979,1988). 

The majority of reactions catalyzed by horseradish peroxidase can be summarized by Eq. (1), in which AH2 represents a reducing substrate. 

Other orchid metabolites suchs as batatasin 1, inhibited the growth of liverworts, algae and oat coleoptiles. Batatasin 1 also inhibited the CO2 dependent O2 evolution and the flow of electrons from water to methylvi-ologen in spinach chloroplasts, and it inhibited the succinate-dependent O2 uptake in potato tuber mitochondria. Other phenanthrenes such as orchinol, which has a free hydroxyl at the 7-position, inhibit indole-3-acetic acid (lAA) oxidation catalyzed by horseradish peroxidase. 

Among other in vitro enzymatic polymerizations that have been studied are the oxidative polymerizations of 2,6-disubstituted phenols to poly(p-phenylene oxide)s (Sec. 2-14b) catalyzed by horseradish peroxidase [Higashimura et al., 2000b] and the polymerization of P-cellobiosyl fluoride to cellulose catalyzed by cellulase [Kobayashi, 1999 Kobayashi et al., 2001],... 

The mechanism of metabolic degradation of indol-3-ylacetic acid (39) is a matter of debate. A possible route demonstrated in vitro includes oxidative decarboxylation to skatolyl hydroperoxide (40), catalyzed by horseradish peroxidase isoenzyme C (HRP-C), followed by rearrangement to 3-(hydroxymethyl)oxindole (41), as shown in equation 12 . 

Akkara JA, Senecal KJ, Kaplan DL (1991) Synthesis and characterization of polymers produced by horseradish peroxidase in dioxane. J Polym Sci A Polym Chem 29 1561-1574... 

Based partly on UV-vis absorption but mostly on surface-enhanced Raman scattering (SERS) data, the electrochemical oxidation product from 9-hydroxyellipticine (9-OH-E) 13a at Pt and Ag electrodes and that from A -methyl-9-hydroxyellipticinium cation (NMHE) 13b at those electrodes and also by horseradish peroxidase-H2O2 were studied and their structures identified <1996JRS539>. The products, 9-oxoellipticine (9-oxo-E) 14a from 9-OH-E and A -methyl-9-oxoellipticinium cation (NMOE) 14b from NMHE both have quinone-imine structures readily identified from the vibrational analysis of their SERS spectra. 

De Rycker, J. Halliwell, B. (1978) Oxidation of 2-nitropropane by horseradish peroxidase. Involvement of hydrogen peroxide and of superoxide in the reaction mechanism. Biochem. J., 175, 601-606... 

Thorpe, G H. G and Kricka, L. J. (1986) Enhanced chemiluminescent reactions catalyzed by horseradish peroxidase. Methods Enzymol. 133, 331-354. 

Laurenti E, Ghibaudi E, Ardissone S, Ferrari RP (2003) Oxidation of 2,4-Dichlorophenol Catalyzed by Horseradish Peroxidase Characterization of the Reaction Mechanism by UV-Visible Spectroscopy and Mass Spectrometry. J Inorg Biochem 95 171... 

Ferrari RP, Laurenti E, TrottaF (1999) Oxidative 4-Dechlorination of 2,4,6-Trichlorophe-nol Catalyzed by Horseradish Peroxidase. J Biol Inorg Chem 4 232... 

Simultaneous detection of three antigens within one tissue section became possible by employing an additional peroxidase substrate such as the Vector VIP Substrate kit (Vector Lab, Burlingham, CA) (Pujic et al., 1998). This substrate is oxidized by horseradish peroxidase and yields a rose-colored final reaction product which differs in color from that... 

Essentially, the CARD protocol is based on the deposition of haptenized tyramide molecules in the vicinity of hybridized probes catalyzed by horseradish peroxidase. The success of this technique depends on the integrity of target mRNA in sections and the ability of the probe to penetrate the sections and hybridize with mRNAs. Another requirement is an efficient reporter system capable of revealing low numbers of probe-mRNA hybrids per cell accompanied by low background staining. 

The rates of asymmetric sulfoxidation of thioanisole in nearly anhydrous (99.7%) isopropyl alcohol and methanol catalyzed by horseradish peroxidase (HRP) were determined to be tens to hundreds of times faster than in water under otherwise identical conditions (Dai, 2000). Similar effects were observed with other hemo-proteins. This dramatic activation is due to a much higher substrate solubility in organic solvents than in water and occurs even though the intrinsic reactivity of HRP in isopropyl alcohol and in methanol is hundreds of times lower than in water. In addition, the rates of spontaneous oxidation of the model prochiral substrate thioanisole in several organic solvents was observed to be some 100- to 1000-fold slower than in water. This renders peroxidase-catalyzed asymmetric sulf-oxidations synthetically attractive. 

Hydroxylation of clavine alkaloids in vitro can be brought about by horseradish peroxidase using hydrogen peroxide as the oxidant, and numerous other tissues (70). This leads only to 8-hydroxylation, e.g., no elymoclavine (54) can be detected from 53. On the other hand, this hydroxylation step also occurs in ergot as a minor metabolic pathway, but it will not be considered here in detail. The reader is referred to the review articles of Voigt (55-57) and of Ramstad (70). 

Chemiluminescence of oxidized luminol has been the basis of several lumino-metric methods of estimation of TAC (Table 1). The mostcommon is to measure the induction time of the reaction. Often the chemiluminescence is first induced by an oxidant and then attenuated by addition of a sample, and the time to recover the initial fluorescence is measured. The enhanced chemiluminescent assay introduced a decade ago is based on the oxidation of luminol by perborate or by hydrogen peroxide in a reaction catalyzed by horseradish peroxidase. Enhancement (and stabilization) of luminescence is achieved by addition of p-iodophenol. The original procedure used a commercial reagent kit (ECL Anti-oxidant Detection Pack... 

---