Horseradish peroxidase, ascorbic acid

APX, ascorbate peroxidase PJiP, Arthromyces ramosus peroxidase BPl, barley grain peroxidase CCP, C3dochrome c peroxidase CIP, Coprinus cinereus peroxidase EXAFS, extended X-ray absorption fine structure HRP, horseradish peroxidase HRP Z (where Z = A1-A3, B1-B3, Cl, C2, D, E1-E6, or N), a specific isoenzyme of horseradish peroxidase HS, high-spin lAA, indole-3-acetic acid LIP, hgnin peroxidase LS, low-spin PNP, the major cationic isoenzyme of peanut peroxidase WT, wild-type 5-c, five-coordinate 6-c, six-coordinate. 

Besides using the bioactive agent to detect the ion of interest, another approach can include monitoring an ion by its inhibitory effect upon enzymatic activity. For example, horseradish peroxidase (HRP) can be immobilised onto one gate of a REFET [107] allowing the presence of cyanide ion to be measured at concentrations of 10 3-10 7 M. The approach used here is to monitor the inhibition of the enzymatic HRP effect, by the cyanide ion, on ascorbic acid. Even lower levels (10 10 M) of detection can be obtained using a polyphenol oxidase/clay composite immobilised on carbon, with no interference from chloride, nitrate or bromide [108]. 

GROB, K., MATILE, P., Compartmentation of ascorbic acid in vacuoles of horseradish root cells. Note on vacuolar peroxidase., Z. Pflanzenphysiol., 1980,98,235-243. 

CV measurements of the modified brushes showed the typical electrochemical response corresponding to a surface-confined electroactive species and the redox counterions, as ferriq anide species form stable ion pairs with the quaternary ammonium groups of the brush (Fig. 4.6] [47]. In a noncovalent way, Mao et al. have reported that ILs could be directly immobilized on the glassy carbon electrode (GC] by casting and observed the electrocatalytic activity toward ascorbic acid (AA] and the capability to facilitate direct electron transfer of horseradish peroxidase (HRP] (Fig. 4.7]... 

Abstract The in vitro enzyme-mediated polymerization of vinyl monomers is reviewed with a scope covering enzymatic polymerization of vitamin C functionalized vinyl monomers, styrene, derivatives of styrene, acrylates, and acrylamide in water and water-miscible cosolvents. Vitamin C functionalized polymers were synthesized via a two-step biocatalytic approach where vitamin C was first regioselectively coupled to vinyl monomers and then subsequently polymerized. The analysis of this enzymatic cascade approach to functionalized vinyl polymers showed that the vitamin C in polymeric form retained its antioxidant property. Kinetic and mechanistic studies revealed that a ternary system (horseradish peroxidase, H2O2, initiator fS-diketone) was required for efficient polymerization and that the initiator controls the characteristics of the polymer. The main attributes of enzymatic approaches to vinyl polymerization when compared with more traditional synthetic approaches include facile ambient reaction environments of temperature and pressure, aqueous conditions, and direct control of selectivity to generate functionalized materials as described for the ascorbic acid modified polymers. 

Recently a new strategy was developed whereby a nuld and highly selective enzymatic method was used to covalently couple the primary hydroxyl group of ascorbic acid with styrene and methyl acrylate monomers, followed by a second enzymatic reaction catalyzed by horseradish peroxidase to polymerize the styrene and acrylate monomers yielding vitamin C functionalized... 

This is not the case with hydroquinone which, therefore, is not suitable for this type of assay. Pyrogallol cannot be used either because of the multistep formation of its colored products. Ascorbic acid and leucomala-chite green can be employed if the choice of pH is not limited and if the correct pH is carefully controlled. In summa, it may be stated that, at least as far as horseradish peroxidase is concerned, the experimental data favor the choice of guaiacol for use in a standard peroxidase assay. 

It should be noted that it is not always possible to satisfy the inequalities kiXo kiOa and x<,< oo, for this implies that ki kt. With polyphenols and aminophenols, as donors for horseradish peroxidase, this is usually not possible, but with less active donors, such as phenol, p-aminobenzoic acid, ascorbic acid, and nitrous acid (near neutral pH), the requirement At is satisfied and zero-order kinetics are obtained (see Table VI in reference 3). If catalase reacts peroxidatically, alcohols and nitrous and formic acids (at neutral pH) satisfy the inequality. 

Fig. 1. This illustrates the zero-order reaction kinetics of the oxidation of ascorbic acid by horseradish peroxidase-hydrogen peroxide complex. The disappearance of hydrogen peroxide upon the addition of 3 mM ascorbic acid is recorded by means of the platinum microelectrode (Expt. 574e).

Fig. 8B. The spectrophotometric recording of the kinetics of peroxidase complex II at 390 m/i and the disappearance of donor (ascorbic acid) at 268 mft. 0.37 iiM horseradish peroxidase, 1.1 nM HtCh, 17 itM ascorbic acid, 0.01 M acetate buffer, pH 4.6 (Expt. 409b).

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