Heme-Containing Plant Peroxidases

Conserved histidine-containing sequences were recognised at an early stage as the probable heme-linked sequences in classical plant peroxidases (Welinder and Mazza, 1977). Similar sequences were later found in CCP (Ihkio et al., 1980) and recently in... 

Peroxidases fall into two superfamilies (plant and mammalian) and a third, indistinct group that includes chloroperoxidase (a P450-like hybrid) and di-heme cytochrome c peroxidase from Pseudomonas aeruginosa. The plant peroxidase superfamily contains enzymes of plant, fungal, and bacterial origin [126], Mammalian peroxidases make up the second superfamily, and include lactoperoxidase, myeloperoxidase, and prostaglandin H synthase. Both families have been the focus of numerous excellent reviews, several of which have discussed the differences between the plant and mammalian peroxidases [126-130], Here, recent experimental investigations focused on the plant peroxidases will be discussed. 

Another example on fluorescence lifetimes of beinoproteins peroxidases (donor H2O2, oxidoreductase E.C. 1.11.1.7) are heme enzymes that catalyze oxidative reactions that use hydrogen perox dase as an electron acceptor. The seed coat soybean peroxidase (SBP) belongs to class III of the plant peroxidase super family, which includes horseradish (HRP), barely (BPl) and peanut (PNP) peroxidases. All the en mes of this class contain a protoheme located within a pocket that plays an important role in the catalytic cycle. Soybean peroxidase (SBP) is a glycoprotein of molecular mass equal to 37 kDa. It is a monomer composed of 326 amino acids with a single tryptophan at position 117 (Figure 7.15). 

The phenoloxidases are a related group of copper containing enzymes that catalyze the oxidation of phenols to quinones in animals and plants (5,6). Two distinct types of phenoloxidases that have substrate specificities and inhibitor sensitivities resembling typical tyrosinases and laccases are found in different types of insect cuticle (Z 8). Peroxidases, heme-containing enz)niies that also oxidize diphenols to quinones, may be present in cuticle and may play a role in sclerotization (9,10). 

It can be seen that yeast and the plant peroxidases which all contain ferriprotoporphyrin IX behave similarly with a consistent trend in all results. Lactoperoxidase with a heme group of unknown structure behaves much differently in its ligand binding reactions and metmyoglobin (which also contains ferriprotoporphyrin IX) cannot be fit into any peroxidase pattern. In all cases for the peroxidases it is the electrically neutral (protonated) form of the ligand which reacts (see Appendix). For the yeast and plant peroxidases the results for H2O2, HF and HN3 indicate that a dissociative... 

Peroxidases (E.C. 1.11.1.7) are ubiquitously found in plants, microorganisms and animals. They are either named after their sources, for example, horseradish peroxidase and lacto- or myeloperoxidase, or akin to their substrates, such as cytochrome c, chloro- or lignin peroxidases. Most of the peroxidases studied so far are heme enzymes with ferric protoporphyrin IX (protoheme) as the prosthetic group (Fig. 1). However, the active centers of some peroxidases also contain selenium (glutathione peroxidase) [7], vanadium (bromoperoxidase)... 

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