Horseradish peroxidase: a modern view of a classic enzyme

Horseradish peroxidase is an important heme-containing enzyme that has been studied for more than a century. In recent years new information has become available on the three-dimensional structure of the enzyme and its catalytic intermediates, mechanisms of catalysis and the function of specific amino acid residues. Site-directed mutagenesis and directed evolution techniques are now used routinely to investigate the structure and function of horseradish peroxidase and offer the opportunity to develop engineered enzymes for practical applications in natural product and fine chemicals synthesis, medical diagnostics and bioremediation. A combination of horseradish peroxidase and indole-3-acetic acid or its derivatives is currently being evaluated as an agent for use in targeted cancer therapies. Physiological roles traditionally associated with the enzyme that include indole-3-acetic acid metabolism, cross-linking of biological polymers and lignification are becoming better understood at the molecular level, but the involvement of specific horseradish peroxidase isoenzymes in these processes is not yet clearly defined. Progress in this area should result from the identification of the entire peroxidase gene family of Arabidopsis thaliana, which has now been completed. # 2003 Elsevier Ltd. All rights reserved.

Molecules of interest Horseradish peroxidase: a modern view of a classic enzyme

I INTRO DUCTION . . . . . . ...... . . . . . . ...... . . . . . . . . . . .. . . . .. . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . 455 1.1 Criteria of Lignin Detection . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . .. . . . 457 1.2 Lignin Distribution in the Plant Kingdom: A Reevaluation . . . . . . . . . . . . . . . . . . . . . . . . . 458 1.3 Lignin Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 462 2 LIGNIN B IOG ENE SI S AND S TRUCT URE.... .. ... . . .. . . . . . .. . . . . . . . . .. . . . . . . .. . . . ...... . . . 469 2.1 Arogenic Acid . . . . . . . . . . . . . . . . . . . .. . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . """'"'''''''''''''''''''' 470 2.2 p-Coumaric Acid to £and Z-Monolignols. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 471 2.3 Monolignol Transport into the Cell Wall . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . .. . . . . . . . . . . . . . 472 2.4 Lignin Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . .. . . . . . . . . . . . . . . . . . . . .. .. .. . .... . . . . . . . . 473 2.5 Regulation of Lignification . . . . . . . . . . . . . . . . . . . . . . . . .. . " . . "" . . . . . . . . . . . . . . . . . . . . . . ". . . . . . 476 2.6 Lignin Structure . . . . . . . . . . . . . . . . . . . . . . . . . . .. . .. . . . . . . . . . . . . . . . .. .. . . . .. . . . . . . . . . . . . . . . . . . . . . . . 477 3 LIGNIN BIO DEGRADATION . . . . . ..... . .... .. . . . . . . . . . . . . . ..... . . . . . . . . . . . . . . . . . . . . .. . 481 3.1 Lignin-like Polymers in White-Rot Fungi .. .. . . . . . . . . . . . . . . . . . . .. .. . . . . . .. ... . .... . . . . . . 481 3.2 Criteria of Lignin Degradation . . . . . . . . .. . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 481 3.3 Lignin Biodegradation by White-Rot Fungi ...... " . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . 482 CONCLU SIONS 487

Lignin: Occurrence, Biogenesis and Biodegradation

A generalized two-step and interdependent control of basic and acidic peroxidases (EC 1.11.1.7) is observed in plant responses to different physical and chemical stimuli. An interpretative model consisting of a pathway of reactions is presented on the basis of our own data and the literature. Stress-induced membrane depolarization would generate different species of free radicals and peroxides, which in turn initiate lipid peroxidation. The degradation of cell membranes is suggested to bring about rapid changes in ionic fluxes (especially release of K+ which would result in an enhanced endogenous Ca/K ratio) and in leakage of solutes (among them electron donors such as ascorbic acid and phenolic substances). The increased intracellular relative calcium level results in: 1) activated secretion of basic peroxidases into the free space where, in association with the electron donors and maybe with the circulating indole-3-acetic acid (IAA), they eliminate the peroxides; and 2) facilitated binding of basic peroxidases to membrane structures allowing a role as 1-aminocyclopropane-1-carboxylic acid (ACC)-oxidases. The resulting IAA and ACC oxidase-mediated changes in ethylene production would further induce (this time through the protein synthesis machinery) an increase in activity of phenylalanine ammonia-lyase (EC 4.31.5) and acidic peroxidases. The resulting lignification and cell wall rigidification determines the growth and/or the developmental response to the initial stress.

A two‐step control of basic and acidic peroxidases and its significance for growth and development

The effect of ozone was studied on the peroxidase activity from various compartments of Sedum album leaves (epidermis, intercellular fluid, residual cell material, and total cell material). The greatest increase following a 2-hour ozone exposure (0.4 microliters O/sub 3/ per liter) was observed in extracellular peroxidases. Most of the main bands of peroxidase activity separated by isoelectric focusing exhibited an increase upon exposure to ozone. Incubation experiments with isolated peeled or unpeeled leaves showed that leaves from ozone-treated plants release much more peroxidases in the medium than untreated leaves. The withdrawal of Ca/sup 2 +/ ions reduced the level of extracellular peroxidase activity either in whole plants or in incubation experiments. This reduction and the activation obtained after addition of Ca/sup 2 +/ resulted from a direct requirment of Ca/sup 2 +/ by the enzyme and from an effect of Ca/sup 2 +/ on peroxidase secretion. The ionophore A23187 promoted an increase of extracellular peroxidase activity only in untreated plants. The release of peroxidases by untreated and ozone-treated leaves is considerably lowered by metabolic inhibitors (3-(3,4-dichlorophenyl)-1,1-dimethylurea and sodium azide) and by puromycin.

H. Greppin

Papers

Peroxidases 1970-1980. A survey of their biochemical and physiological roles in higher plants.

Auxin control of calcium mediated peroxidase ec 1.11.1.7 secretion by auxin dependent and auxin independent sugar beet beta vulgaris cells