Horseradish isoenzyme

Strickland, E., Hardin, E.K., Shannon, L.M., and Horwitz, J. (1968) Peroxidase isoenzymes from horseradish roots. III. Circular dichroism of isoenzymes and apoisoenzymes. J. Biol. Chem. 243, 3560. 

The catalysis mechanism of horseradish PX and, in particular, the C isoenzyme, has been investigated extensively. However, although there is a wide range of PX isoenzymes, the following equation describes most of the reactions catalyzed by PX ... 

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. 

Expression of peroxidases that catalyze crosslinking reactions can he induced by wounding or infection. Well-documented examples include the production of acidic peroxidase isoenzymes in woimded tissue of tobacco (132), potato (133), and tomato (134), and also in wheat plants infected with the powdery mildew fungus, Erysiphe graminis (135). It is known that peroxidase activity can be induced on wounding of horseradish leaves (56), but other mechanisms of defense in horseradish remain to be demonstrated. 

The presence of calcium in horseradish peroxidase was demonstrated originally by Haschke and Friedhoff, working with the C and A (imspec-ified, but likely to have been predominantly A2) isoenzymes (209). HRP C and HRP A contain 2.0 0.13 and 1.4 0.19 moles calcium per mole enzyme, respectively, as determined by atomic absorption spectroscopy. Incubation in 6 M guanidinium hydrochloride and 10 mM EDTA for 4 hours at neutral pH and room temperature gave calcium-depleted enzymes with specific activities decreased by 40% and 15%, respectively. The thermal stability of calcium-depleted HRP C was also reduced compared to native enzyme. Reconstitution was successful only with calcium-depleted HRP C (209). It remains to be established whether this reflects true structural differences between the calcium binding sites of the two isoenz5unes, or is a consequence of the relatively harsh... 

Zhao, D., Gilfoyle, D. J., Smith, A. T., and Loew, G. H. (1996) Refinement of 3D models of horseradish peroxidase isoenzyme C predictions of 2D NMR assignments and substrate binding sites. Proteins 26, 204-216. 

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 . 

However, it should be noted that isoenzymes, i.e., different enzymes catalyzing identical reactions, would have the same four-digit classification. The classification system provides only the basis for a unique identification of an enzyme the particular isoenzyme and its source still have to be specified. For example, peroxidases isolated from soybeans and horseradishes have the same classification, i.e., EC 1.11.1.7. Currently, there are approximately 3200 enzymes that have been listed and assigned classification numbers. 

Rodriguez-Lopez JN, Smith AT, Thomeley RNF (1996) Recombinant horseradish peroxidase isoenzyme C the effect of distal haem cavity mutations (His42->Leu and Arg38->Leu on compound I formation and substrate binding. J Biol Inorg Chem 1 136-142... 

Generation of CIII from GS occurs when the enzyme acts as an oxidase in the presence of superoxide ion. This reaction has been observed in horseradish peroxidase isoenzymes C and A2 [28, 53, 63], lignin peroxidase [46], myeloperoxidase [69], and bovine liver catalase [64], The rate constant for the reaction of GS with superoxide increases with a decrease of pH suggesting that the reacting species is HO2 instead of C - [64], The physiological relevance of the hydroxyperoxyl radical has been recently reassessed [70],... 

Berglund et al. reported the 1.6 A structure of CIII of recombinant horseradish peroxidase C isoenzyme as part of a multicrystal data collection strategy aimed to the visualization of the peroxidasic catalytic pathway at atomic levels... 

Hiner AN, Hemandez-Ruiz J, Garcia-Canovas F et al (1995) A comparative study of the inactivation of wild-type, recombinant and two mutant horseradish peroxidase isoenzymes C by hydrogen peroxide and m-chloroperoxybenzoic acid. Eur J Biochem 234 506-512... 

Affinity constants (KM) for some horseradish peroxidase isoenzymes. 337... 

Physicochemical properties of horseradish peroxidase isoenzymes Isoenzyme Mw Carbohydrate pi s (mVP cm ) References... 

Hiner ANP, Hemandez-Rtuz J, Amao MB et al (1996) A comparative study of the purity, enzyme activity, and inactivation by hydrogen peroxide of commercially available horseradish peroxidase isoenzymes A and C. Biotechnol Bioeng 50 655-662... 

Aibara S, Yamashita H, Mori E et al (1982) Isolation and characterization of five neutral isoenzymes of horseradish peroxidase. J Biochem 92 531-539... 

Aibara S, Kobayashi T, Morita Y (1981) Isolation and properties of basic isoenzymes of horseradish peroxidase. J Biochem 90 489-496... 

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